soc: imx8m: Probe the SoC driver as platform driver

soc: imx8m: Probe the SoC driver as platform driver

With driver_async_probe=* on kernel command line, the following trace is
produced because on i.MX8M Plus hardware because the soc-imx8m.c driver
calls of_clk_get_by_name() which returns -EPROBE_DEFER because the clock
driver is not yet probed. This was not detected during regular testing
without driver_async_probe.

Convert the SoC code to platform driver and instantiate a platform device
in its current device_initcall() to probe the platform driver. Rework
.soc_revision callback to always return valid error code and return SoC
revision via parameter. This way, if anything in the .soc_revision callback
return -EPROBE_DEFER, it gets propagated to .probe and the .probe will get
retried later.

"
------------[ cut here ]------------
WARNING: CPU: 1 PID: 1 at drivers/soc/imx/soc-imx8m.c:115 imx8mm_soc_revision+0xdc/0x180
CPU: 1 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.11.0-next-20240924-00002-g2062bb554dea #603
Hardware name: DH electronics i.MX8M Plus DHCOM Premium Developer Kit (3) (DT)
pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : imx8mm_soc_revision+0xdc/0x180
lr : imx8mm_soc_revision+0xd0/0x180
sp : ffff8000821fbcc0
x29: ffff8000821fbce0 x28: 0000000000000000 x27: ffff800081810120
x26: ffff8000818a9970 x25: 0000000000000006 x24: 0000000000824311
x23: ffff8000817f42c8 x22: ffff0000df8be210 x21: fffffffffffffdfb
x20: ffff800082780000 x19: 0000000000000001 x18: ffffffffffffffff
x17: ffff800081fff418 x16: ffff8000823e1000 x15: ffff0000c03b65e8
x14: ffff0000c00051b0 x13: ffff800082790000 x12: 0000000000000801
x11: ffff80008278ffff x10: ffff80008209d3a6 x9 : ffff80008062e95c
x8 : ffff8000821fb9a0 x7 : 0000000000000000 x6 : 00000000000080e3
x5 : ffff0000df8c03d8 x4 : 0000000000000000 x3 : 0000000000000000
x2 : 0000000000000000 x1 : fffffffffffffdfb x0 : fffffffffffffdfb
Call trace:
 imx8mm_soc_revision+0xdc/0x180
 imx8_soc_init+0xb0/0x1e0
 do_one_initcall+0x94/0x1a8
 kernel_init_freeable+0x240/0x2a8
 kernel_init+0x28/0x140
 ret_from_fork+0x10/0x20
---[ end trace 0000000000000000 ]---
SoC: i.MX8MP revision 1.1
"

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>