ARM: vexpress: fix ll debug code when building multiplatform

After "ARM: vexpress: Make the debug UART detection more specific",
building allyesconfig in linux-next now gives me:

arch/arm/kernel/debug.S: Assembler messages:
arch/arm/kernel/debug.S:81: Error: selected processor does not support ARM mode `movw r2,#0xc 091'
arch/arm/kernel/debug.S:81: Error: selected processor does not support ARM mode `movt r2,#0x4 10f'
arch/arm/kernel/debug.S:97: Error: selected processor does not support ARM mode `movw r2,#0xc 091'
arch/arm/kernel/debug.S:97: Error: selected processor does not support ARM mode `movt r2,#0x4 10f'
arch/arm/kernel/debug.S:104: Error: selected processor does not support ARM mode `movw r3,#0x c091'
arch/arm/kernel/debug.S:104: Error: selected processor does not support ARM mode `movt r3,#0x 410f'

Since the code can never get executed on ARMv6 but might
be built in a configuration that has ARMv6 enabled, it's
safe to just mark it in the assembly source for being
ARMv7-only.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Pawel Moll <pawel.moll@arm.com>

arch/arm/include/debug/vexpress.S

@@ -21,6 +21,7 @@
 #if defined(CONFIG_DEBUG_VEXPRESS_UART0_DETECT)
 
 		.macro	addruart,rp,rv,tmp
+		.arch   armv7-a
 
 		@ Make an educated guess regarding the memory map:
 		@ - the original A9 core tile (based on ARM Cortex-A9 r0p1)