drm/amd/display: Adjust static-ness of resource functions

[Why]
Register definitions are asic-specific, so functions that use registers of
a particular asic should be static, to be exposed in asic-specific function
pointer structures.

[How]
 - make register-definition-using functions static
 - make some functions non-static, for future use
 - remove duplicate function definition

Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>