drm/amd/display: Poll for GPUVM context ready (v2)
[Why]
Hardware docs state that we must wait until the GPUVM context is ready
after programming it.
[How]
Poll until the valid bit of PAGE_TABLE_BASE_ADDR_LO32 is set to 1 after
programming it.
v2: fix include for udelay (Alex)
Signed-off-by: Julian Parkin <julian.parkin@amd.com> Reviewed-by: Charlene Liu <Charlene.Liu@amd.com> Acked-by: Leo Li <sunpeng.li@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>