drm/amd/display: fix some coding style issues

Fix the following checkpatch checks in amdgpu_dm.c

CHECK: Prefer kernel type 'u8' over 'uint8_t'
CHECK: Prefer kernel type 'u32' over 'uint32_t'
CHECK: Prefer kernel type 'u64' over 'uint64_t'
CHECK: Prefer kernel type 's32' over 'int32_t'

Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>