ARM: shmobile: always build rcar setup for armv7

In a combined ARMv6/v7 kernel, the setup-rcar-gen2.c cannot
currently be compiled correctly because it uses the isb
instruction that is not available on ARMv6. Adding the
-march=armv7-a flag lets the compiler know that it is safe
to build this file for ARMv7.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>