vk: Make batch chain code gen-agnostic
vk: Make batch chain code gen-agnostic

Since the extra dword in MI_BATCH_BUFFER_START added in gen8 is at the
end of the struct, we can emit the gen8 packet on all gens as long as we
set the instruction length correctly.

Signed-off-by: Kristian Høgsberg Kristensen <4b441a45a1cdbce08ca0aaabb01d554a77184d64@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler