intel/common/intel_genX_state.h: Add intel_set_ps_dispatch_state()

intel/common/intel_genX_state.h: Add intel_set_ps_dispatch_state()

This replaces brw_fs_get_dispatch_enables(), which was added in
b9403b1c477 ("intel: factor out dispatch PS enabling logic"), but this
function will not work well for future changes to 3DSTATE_PS.

So, instead, this moves the related code into a "genX" file which can
directly update 3DSTATE_PS for the given platform.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20329>