i965/tiled_memcpy: avoid creating bswap32 if it exists as a macro (e.g. on FreeBSD)

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>

src/intel/isl/isl_tiled_memcpy.c

@@ -64,6 +64,8 @@ ror(uint32_t n, uint32_t d)
    return (n >> d) | (n << (32 - d));
 }
 
+// bswap32 already exists as a macro on some platforms (FreeBSD)
+#ifndef bswap32
 static inline uint32_t
 bswap32(uint32_t n)
 {
@@ -76,6 +78,7 @@ bswap32(uint32_t n)
           (n << 24);
 #endif
 }
+#endif
 
 /**
  * Copy RGBA to BGRA - swap R and B.