drm/amdkfd: add hqd_sdma_get_doorbell callbacks for gfx7/8

drm/amdkfd: add hqd_sdma_get_doorbell callbacks for gfx7/8

These were missed when support was added for other generations.
The callbacks are called unconditionally so we need to make
sure all generations have them.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4304
Link: https://github.com/ROCm/ROCm/issues/4965
Fixes: bac38ca8c475 ("drm/amdkfd: implement per queue sdma reset for gfx 9.4+")
Cc: Jonathan Kim <jonathan.kim@amd.com>
Reported-by: Johl Brown <johlbrown@gmail.com>
Reviewed-by: Jonathan Kim <jonathan.kim@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>