ARM: 9039/1: assembler: generalize byte swapping macro into rev_l

Take the 4 instruction byte swapping sequence from the decompressor's
head.S, and turn it into a rev_l GAS macro for general use. While
at it, make it use the 'rev' instruction when compiling for v6 or
later.

Reviewed-by: Geert Uytterhoeven <[e-mail]>
Tested-by: Geert Uytterhoeven <[e-mail]>
Reviewed-by: Nicolas Pitre <[e-mail]>
Signed-off-by: Ard Biesheuvel <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/boot/compressed/head.S

···
 		.macro	be32tocpu, val, tmp
 #ifndef __ARMEB__
 		/* convert to little endian */
-		eor	\tmp, \val, \val, ror #16
-		bic	\tmp, \tmp, #0x00ff0000
-		mov	\val, \val, ror #8
-		eor	\val, \val, \tmp, lsr #8
+		rev_l	\val, \tmp
 #endif
 		.endm
 

arch/arm/include/asm/assembler.h

···
 	__adldst_l	str, \src, \sym, \tmp, \cond
 	.endm
 
+	/*
+	 * rev_l - byte-swap a 32-bit value
+	 *
+	 * @val: source/destination register
+	 * @tmp: scratch register
+	 */
+	.macro		rev_l, val:req, tmp:req
+	.if		__LINUX_ARM_ARCH__ < 6
+	eor		\tmp, \val, \val, ror #16
+	bic		\tmp, \tmp, #0x00ff0000
+	mov		\val, \val, ror #8
+	eor		\val, \val, \tmp, lsr #8
+	.else
+	rev		\val, \val
+	.endif
+	.endm
+
 #endif /* __ASM_ASSEMBLER_H__ */