iris: Use 3DSTATE_CONSTANT_ALL when possible.

iris: Use 3DSTATE_CONSTANT_ALL when possible.

Use this new instruction introduced in Gen12. The instruction itself is
smaller, and it also allows us to emit a single instruction to all
stages that have the same push constant buffers (e.g. when they don't
have constant buffers).

There's one restriction to use this instruction, though: the length
field is only 5 bits long, so we need to check whether we can use it,
and fallback to the old 3DSTATE_CONSTANT_XS if that field is >= 32.

v2 (Suggestions from Caio):
 - use max_length instead of large_buffers.
 - remove UNUSED and use #if GEN_GEN >= 12 instead.
 - inline "buffers" and drop BITSET_RANGE() usage.
 - add assert(n <= max_pointers)
 - move emit to outside of the loop.

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