intel/fs: Implement the new load/store_scratch intrinsics

intel/fs: Implement the new load/store_scratch intrinsics

This commit fills in a number of different pieces:

 1. We add support to brw_nir_lower_mem_access_bit_sizes to handle the
    new intrinsics.  This involves simple plumbing work as well as a
    tiny bit of extra logic to always scalarize scratch intrinsics

 2. Add code to brw_fs_nir.cpp to turn nir_load/store_scratch intrinsics
    into byte/dword scattered read/write messages which use the A32
    stateless model.

 3. Add code to lower_surface_logical_send to handle dword scattered
    messages and the A32 stateless model.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>