drm/amdgpu: change reset lock from mutex to rw_semaphore

drm/amdgpu: change reset lock from mutex to rw_semaphore

clients don't need reset-lock for synchronization when no
GPU recovery.

v2:
change to return the return value of down_read_killable.

v3:
if GPU recovery begin, VF ignore FLR notification.

Reviewed-by: Monk Liu <monk.liu@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dennis Li <Dennis.Li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>