ARM: 8801/1: makefile: use ARMv3M mode for RiscPC

The purpose of CONFIG_CPU_32v3 is to avoid ldrh/strh on the RiscPC,
which is pretty much an ARMv4 device, except its bus will choke on the
half-words. The way to make the C compiler not output ldrh/strh is with
-march=armv3, which doesn't support them in the ISA. However, this
prevents certain cryptography code from working that uses instructions
like umull. Fortunately there's also -march=armv3m that does support
those, making it possible to continue assembling optimized cryptography
routines for our beloved RiscPC.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>