[ARM] 5269/1: ARMv7: Use -march=armv7-a as compiler flag

The current -march=armv7a is not supported by mainline gcc.

Cc: Paul Brook <paul@codesourcery.com>
Cc: Wei Zhong <weizhong@broadcom.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>