Some systems compile in both ARMv6 and ARMv7 into multiplatform
configurations. This means the default compiler flags are for ARMv6,
and we will get:

arch/arm/mach-mvebu/coherency_ll.S: Assembler messages:
arch/arm/mach-mvebu/coherency_ll.S:45: Error: selected processor does not support `dsb'

Fix this by specifying ARMv7 flags for coherency_ll.o.
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Olof Johansson <olof@lixom.net>