util/bitset: add a new last bit api

This is to be used where the bitset is a predefined array size.

Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9456>

src/util/bitset.h

@@ -109,6 +109,7 @@ __bitset_last_bit(const BITSET_WORD *x, int n)
 }
 
 #define BITSET_FFS(x) __bitset_ffs(x, ARRAY_SIZE(x))
+#define BITSET_LAST_BIT(x) __bitset_last_bit(x, ARRAY_SIZE(x))
 #define BITSET_LAST_BIT_SIZED(x, size) __bitset_last_bit(x, size)
 
 static inline unsigned