drm/radeon: add get_allowed_info_register for SI

Registers that can be fetched from the info ioctl.

Tested-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --cc drivers/gpu/drm/radeon/radeon_asic.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_asic.h
Simple merge

diff --cc drivers/gpu/drm/radeon/si.c
Simple merge

diff --cc drivers/gpu/drm/radeon/sid.h
Simple merge