drm/amd/display: rework macros for DWB register access

[Why]
A hack was used to access DWB register due to difference in the register
naming convention which was not compatible with existing SR/SRI* macros.
The additional macro needed were added to dwb ip specific header file
(dcnxx_dwb.h) instead of soc resource file (dcnxx_resource.c). Due to
this pattern, BASE macro had to be redefined in dcnxx_dwb.h, which in
turn needed us to undefine them in the resource file.

[How]
Add a separate macro for DWB access to the resource files that need it
instead of defining them in DWB ip header file. This will enable us to
reuse the BASE macro defined in the resource file.

Reviewed-by: Roman Li <Roman.Li@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>