drm/amdgpu: Rename xcc specific functions

Add 'xcc' prefix to xcc specific functions to distinguish from IP block
functions.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>