brw: Move into a new src/intel/compiler/brw subdirectory

This keeps the directory structure a bit more organized:
- brw specific code
- elk specific code
- common NIR passes that could be used in both places

It also means that you can now 'git grep' in the brw directory without
finding a bunch of elk code, or having to "grep thing b*".

Reviewed-by: Dylan Baker <dylan.c.baker@intel.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37755>

src/intel/decoder/intel_batch_decoder_brw.c

@@ -6,7 +6,7 @@
 #include "intel_decoder.h"
 #include "intel_decoder_private.h"
 
-#include "compiler/brw_disasm.h"
+#include "compiler/brw/brw_disasm.h"
 
 static void
 ctx_disassemble_program_brw(struct intel_batch_decode_ctx *ctx,