ARM: 6431/1: fix isb regression on CPU < v7

The kernel does not compile for my ARM926EJ-S system U300 due to
the isb instruction inserted in generic assember statement from
commit 8925ec4, "ARM: 6385/1:
setup: detect aliasing I-cache when D-cache is non-aliasing"
hey the isb is only available when assembling for v7 so let's
use the generic isb() macro from setup.h instead.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/setup.c

@@ -246,11 +246,12 @@ static int cpu_has_aliasing_icache(unsigned int arch)
 	/* arch specifies the register format */
 	switch (arch) {
 	case CPU_ARCH_ARMv7:
-		asm("mcr	p15, 2, %1, c0, c0, 0	@ set CSSELR\n"
-		    "isb\n"
-		    "mrc	p15, 1, %0, c0, c0, 0	@ read CCSIDR"
-		    : "=r" (id_reg)
+		asm("mcr	p15, 2, %0, c0, c0, 0 @ set CSSELR"
+		    : /* No output operands */
 		    : "r" (1));
+		isb();
+		asm("mrc	p15, 1, %0, c0, c0, 0 @ read CCSIDR"
+		    : "=r" (id_reg));
 		line_size = 4 << ((id_reg & 0x7) + 2);
 		num_sets = ((id_reg >> 13) & 0x7fff) + 1;
 		aliasing_icache = (line_size * num_sets) > PAGE_SIZE;