drm/radeon: fix VGT_GS_INSTANCE_CNT register

This register was incorrect for evergreen and cayman.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

diff --cc drivers/gpu/drm/radeon/reg_srcs/cayman
Simple merge

diff --cc drivers/gpu/drm/radeon/reg_srcs/evergreen
Simple merge