ARM: socfpga: fix build break for allyesconfig

Building a multiplatform kernel with combined armv7 and armv6
kernel does not work with the socfpga smp code, which contains
v7-only instructions. Since this code never runs on armv6,
we can annotate the assmebly with .arch   armv7-a, as suggested
by Russell King.

[arnd: reword commit message]
Signed-off-by: NPavel Machek <pavel@denx.de>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>

arch/arm/mach-socfpga/headsmp.S

@@ -11,6 +11,7 @@
 #include <linux/init.h>
 
 	__INIT
+	.arch	armv7-a
 
 #define CPU1_START_ADDR 	        0xffd08010