drm/amd/display: change to runtime initialization for reg offsets for DCN321

DC was using compile time initialization of register addresses using
SR_* macros and their variants. These have been converted to use runtime
initialization.

The REG_STRUCT macro is a definition that is added to SR_* macros.
During initialization, this must be defined before SR_* macros are
invoked, which are in turn invoked through various IP initialization macros.
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Brian Chang <Brian.Chang@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>