arm: mutex: merge Will Deacon's patch for including a different implementationfor mutexes for ARM6+ chips. Didn't cherry pick original patches because they conflicted for some reason and I felt too lazy to fix the conflict.

Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
Signed-off-by: nicholas <firepoison35@gmail.com>

Conflicts:
	arch/arm/include/asm/mutex.h