[ARM] Fix byte order macros for Thumb

The byte order functions are visible to userspace.  Unfortunately,
__arch_swab32() contains an assembly instruction which is invalid when
compiling for Thumb.  This reverts to the C version when compiling for
Thumb.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

include/asm-arm/byteorder.h

@@ -22,16 +22,18 @@ static inline __attribute_const__ __u32 ___arch__swab32(__u32 x)
 {
 	__u32 t;
 
-	if (__builtin_constant_p(x)) {
-		t = x ^ ((x << 16) | (x >> 16)); /* eor r1,r0,r0,ror #16 */
-	} else {
+#ifndef __thumb__
+	if (!__builtin_constant_p(x)) {
 		/*
 		 * The compiler needs a bit of a hint here to always do the
 		 * right thing and not screw it up to different degrees
 		 * depending on the gcc version.
 		 */
 		asm ("eor\t%0, %1, %1, ror #16" : "=r" (t) : "r" (x));
-	}
+	} else
+#endif
+		t = x ^ ((x << 16) | (x >> 16)); /* eor r1,r0,r0,ror #16 */
+
 	x = (x << 24) | (x >> 8);		/* mov r0,r0,ror #8      */
 	t &= ~0x00FF0000;			/* bic r1,r1,#0x00FF0000 */
 	x ^= (t >> 8);				/* eor r0,r0,r1,lsr #8   */