drm/xe: Add config control for svm flush work

drm/xe: Add config control for svm flush work

Without CONFIG_DRM_XE_GPUSVM set, GPU SVM is not initialized thus below
warning pops. Refine the flush work code to be controlled by the config
to avoid below warning:
"
[  453.132028] ------------[ cut here ]------------
[  453.132527] WARNING: CPU: 9 PID: 4491 at kernel/workqueue.c:4205 __flush_work+0x379/0x3a0
[  453.133355] Modules linked in: xe drm_ttm_helper ttm gpu_sched drm_buddy drm_suballoc_helper drm_gpuvm drm_exec
[  453.134352] CPU: 9 UID: 0 PID: 4491 Comm: xe_exec_mix_mod Tainted: G     U  W           6.15.0-rc3+ #7 PREEMPT(full)
[  453.135405] Tainted: [U]=USER, [W]=WARN
...
[  453.136921] RIP: 0010:__flush_work+0x379/0x3a0
[  453.137417] Code: 8b 45 00 48 8b 55 08 89 c7 48 c1 e8 04 83 e7 08 83 e0 0f 83 cf 02 89 c6 48 0f ba 6d 00 03 e9 d5 fe ff ff 0f 0b e9 db fd ff ff <0f> 0b 45 31 e4 e9 d1 fd ff ff 0f 0b e9 03 ff ff ff 0f 0b e9 d6 fe
[  453.139250] RSP: 0018:ffffc90000c67b18 EFLAGS: 00010246
[  453.139782] RAX: 0000000000000000 RBX: ffff888108a24000 RCX: 0000000000002000
[  453.140521] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff8881016d61c8
[  453.141253] RBP: ffff8881016d61c8 R08: 0000000000000000 R09: 0000000000000000
[  453.141985] R10: 0000000000000000 R11: 0000000008a24000 R12: 0000000000000001
[  453.142709] R13: 0000000000000002 R14: 0000000000000000 R15: ffff888107db8c00
[  453.143450] FS:  00007f44853d4c80(0000) GS:ffff8882f469b000(0000) knlGS:0000000000000000
[  453.144276] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  453.144853] CR2: 00007f4487629228 CR3: 00000001016aa000 CR4: 00000000000406f0
[  453.145594] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  453.146320] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  453.147061] Call Trace:
[  453.147336]  <TASK>
[  453.147579]  ? tick_nohz_tick_stopped+0xd/0x30
[  453.148067]  ? xas_load+0x9/0xb0
[  453.148435]  ? xa_load+0x6f/0xb0
[  453.148781]  __xe_vm_bind_ioctl+0xbd5/0x1500 [xe]
[  453.149338]  ? dev_printk_emit+0x48/0x70
[  453.149762]  ? _dev_printk+0x57/0x80
[  453.150148]  ? drm_ioctl+0x17c/0x440
[  453.150544]  ? __drm_dev_vprintk+0x36/0x90
[  453.150983]  ? __pfx_xe_vm_bind_ioctl+0x10/0x10 [xe]
[  453.151575]  ? drm_ioctl_kernel+0x9f/0xf0
[  453.151998]  ? __pfx_xe_vm_bind_ioctl+0x10/0x10 [xe]
[  453.152560]  drm_ioctl_kernel+0x9f/0xf0
[  453.152968]  drm_ioctl+0x20f/0x440
[  453.153332]  ? __pfx_xe_vm_bind_ioctl+0x10/0x10 [xe]
[  453.153893]  ? ioctl_has_perm.constprop.0.isra.0+0xae/0x100
[  453.154489]  ? memory_bm_test_bit+0x5/0x60
[  453.154935]  xe_drm_ioctl+0x47/0x70 [xe]
[  453.155419]  __x64_sys_ioctl+0x8d/0xc0
[  453.155824]  do_syscall_64+0x47/0x110
[  453.156228]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
"

v2 (Matt):
    refine commit message to have more details
    add Fixes tag
    move the code to xe_svm.h which already have the config
    remove a blank line per codestyle suggestion

Fixes: 63f6e480d115 ("drm/xe: Add SVM garbage collector")
Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250502170052.1787973-1-shuicheng.lin@intel.com
(cherry picked from commit 9d80698bcd97a5ad1088bcbb055e73fd068895e2)
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>