drm/amd/gfx: add instance field to select_se_sh (v3)

Add ability to specify instance in select_se_sh callback.
Defaults to 0xffffffff all over the driver.

(v2) Don't enable INSTANCE_BROADCAST by default
(v3) Style changes

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>