powerpc/booke: Define MSR bits the same way as reg.h

This ensures that all MSR definitions are consistently unsigned long,
and that MSR_CM does not become 0xffffffff80000000 (this is usually
harmless because MSR is 32-bit on booke and is mainly noticeable when
debugging, but still I'd rather avoid it).

Signed-off-by: Scott Wood <scottwood@freescale.com>