[Why&How]
Add a field to store the DCN IP offset for use with runtime offset
calculation

This offset is indexed using reg*_BASE_IDX for the corresponding
group of registers. For example, address of DIG_BE_CNTL instance 0 is
calculated like: dcn_reg_offsets[regDIG0_DIG_BE_CNTL_BASE_IDX] +
regDIG0_DIG_BE_CNTL.

{dcn,nbio}_reg_offsets are used only for the ASICs for which runtime
initializaion of offsets are enabled through the modified SR* macros
that contain an additional REG_STRUCT element in the macro definition.

DCN3.5+ will fail dc_create() if {dcn,nbio}_reg_offsets are null. They
are applicable starting with DCN32/321 and are not used for ASICs
upstreamed before them. ASICs before DCN32/321 will not contain any
computation that involves {dcn,nbio}_reg_offsets. For them, the
address/offset computation is done during compile time.

This is evident from the BASE_INNER definition for compile time vs run
time initialization:

Compile time init: #define BASE_INNER(seg) DCN_BASE__INST0_SEG ## seg
Run time init:     #define BASE_INNER(seg) ctx->dcn_reg_offsets[seg]

BASE_INNER macro is local to each dcnxx_resource.c and hence different
ASICs can have either runtime or compile time initialization of offsets.

The computation of offset is done for registers all at once during
driver load and hence it does not introduce any performance overhead
during normal operation.
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@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>