ARM: mvebu: Fix pmsu compilation when ARMv6 is selected

ARM: mvebu: Fix pmsu compilation when ARMv6 is selected

When compiling for multiplatform for both ARMv6 and ARMv7, the default compiler
flags are for ARMv6, and we will get:

  /tmp/ccwDEzd0.s: Assembler messages:
  /tmp/ccwDEzd0.s:639: Error: selected processor does not support ARM mode `isb '
  /tmp/ccwDEzd0.s:645: Error: selected processor does not support ARM mode `isb '
  /tmp/ccwDEzd0.s:646: Error: selected processor does not support ARM mode `dsb '
  /tmp/ccwDEzd0.s:695: Error: selected processor does not support ARM mode `isb '
  make[1]: *** [arch/arm/mach-mvebu/pmsu.o] Error 1

Fix this in a similar manner than done previously in commit
72533b77d30c2be02672e26b5dde1263d7b4c2be, by specifying ARMv7 flags for pmsu.o.

Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Link: https://lkml.kernel.org/r/1399407782-29091-1-git-send-email-vincent.stehle@laposte.net
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Gregory Clement <gregory.clement@free-electrons.com>
Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>