[ARM] Fix missing compiler.h include

asm/mach/arch.h introduced a __deprecated, but didn't include compiler.h,
causing:

In file included from arch/arm/mach-at91rm9200/devices.c:13:
include/asm/mach/arch.h:23: warning: no semicolon at end of struct or union
include/asm/mach/arch.h:23: error: syntax error before 'phys_ram'
include/asm/mach/arch.h:34: error: syntax error before ':' token
include/asm/mach/arch.h:35: error: syntax error before ':' token
include/asm/mach/arch.h:36: error: syntax error before ':' token
include/asm/mach/arch.h:37: error: syntax error before ':' token
include/asm/mach/arch.h:45: error: syntax error before '}' token

Add the necessary include.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>