intel/fs/copy-prop: Bump the hash table size to 64

While the number of ACPs is generally not huge compared to the number of
blocks, 16 does seem a bit small.  Bumping it to 64 takes the execution
time of the piglit vs-isnan-dvec test from about 1:18.1 on an unoptimized
debug build (what we run in CI) with NIR_VALIDATE=0 to about 1:16.2.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/intel/compiler/brw_fs_copy_propagation.cpp

@@ -32,7 +32,7 @@
  * 12.5 (p356).
  */
 
-#define ACP_HASH_SIZE 16
+#define ACP_HASH_SIZE 64
 
 #include "util/bitset.h"
 #include "brw_fs.h"