i965: Reorder brw_reg_type enum values

i965: Reorder brw_reg_type enum values

These vaguely corresponded to the hardware encodings, but that is purely
historical at this point. Reorder them so we stop making things "almost
work" when mixing enums.

The ordering has been closen so that no enum value is the same as a
compatible hardware encoding.

Reviewed-by: Scott D Phillips <scott.d.phillips@intel.com>