drm/amdgpu: lock and unlock console only for amdgpu_fbdev_set_suspend [V5]

drm/amdgpu: lock and unlock console only for amdgpu_fbdev_set_suspend [V5]

[Why]
While the console_lock is held, console output will be buffered, till
its unlocked it wont be emitted, hence its ideal to unlock sooner to enable
debugging/detecting/fixing of any issue in the remaining sequence of events
in resume path.
The concern here is about consoles other than fbcon on the device,
e.g. a serial console

[How]
This patch restructures the console_lock, console_unlock around
amdgpu_fbdev_set_suspend() and moves this new block appropriately.

V2: Kept amdgpu_fbdev_set_suspend after pci_set_power_state
V3: Updated the commit message to clarify the real concern that this patch
    addresses.
V4: code clean-up.
V5: fixed return value

Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>