mips: fix implicit smp.h usage in various files.

We need to call out inclusion of smp.h, or with the module.h cleanup
we'll get things like:

arch/mips/loongson/common/platform.c:21: error: implicit declaration of function 'smp_processor_id'

arch/mips/vr41xx/common/giu.c:84: error: implicit declaration of function 'smp_processor_id'

arch/mips/vr41xx/common/rtc.c:85: error: implicit declaration of function 'smp_processor_id'

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>