i965: Add defines for gather push constants
i965: Add defines for gather push constants

v2 (Francisco Jerez):
   - Rename HSW_GATHER_CONSTANTS_RESERVED to HSW_GATHER_POOL_ALLOC_MUST_BE_ONE.
   - Rename BRW_GATHER_* prefix to HSW_GATHER_CONSTANT_*.

Reviewed-by: Francisco Jerez <5906ff32bdd9fd8db196f6ba5ad3afd6f9257ea5@riseup.net>
Signed-off-by: Abdiel Janulgue <b6177409facd0a1ebaf54f9c29b28b2642b3c468@linux.intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler