intel/compiler: Set swizzle to BRW_SWIZZLE_XXXX for scalar region

intel/compiler: Set swizzle to BRW_SWIZZLE_XXXX for scalar region

When RepCtrl is set, the swizzle field is ignored by the hardware. In
order to ensure a 1-to-1 correspondence between the human-readable
disassembly and the binary instruction encoding always set the swizzle
to XXXX (all zeros) when it is unused due to RepCtrl

Signed-off-by: Sagar Ghuge <sagar.ghuge@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>