ARM: findbit: provide more efficient ARMv7 implementation

Provide a more efficient ARMv7 implementation to determine the first
set bit in the supplied value.

Signed-off-by: Russell King (Oracle) <[e-mail]>

arch/arm/lib/findbit.S

···
  * One or more bits in the LSB of r3 are assumed to be set.
  */
 .L_found:
-#if __LINUX_ARM_ARCH__ >= 5
+#if __LINUX_ARM_ARCH__ >= 7
+		rbit	r3, r3			@ reverse bits
+		clz	r3, r3			@ count high zero bits
+		add	r0, r2, r3		@ add offset of first set bit
+#elif __LINUX_ARM_ARCH__ >= 5
 		rsb	r0, r3, #0
 		and	r3, r3, r0		@ mask out lowest bit set
 		clz	r3, r3			@ count high zero bits