ARM: 6126/1: ARM mpcore_wdt: fix build failure and other fixes

This fixes the build failures seen when building mpcore_wdt and it
also removes the nonexistent ARM_MPCORE_PLATFORM dependency, instead
make it dependent on HAVE_ARM_TWD.

Also this fixes spinlock usage appropriately.

Signed-off-by: srinidhi kasagar <srinidhi.kasagar@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>