drm/amd/amdgpu: De-numberify golden SI registers

Where possible replace numeric constants in the table
with their register names.

Compile tested + executed on a Tahiti.
Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>