MSP430: Add mul{hi,si} and {u,}mulsidi3 expanders

MSP430: Add mul{hi,si} and {u,}mulsidi3 expanders

GCC generates better code when multiplication operations, which require
library functions to perform, are caught in early in RTL, rather than
leaving the operation to be mapped to a library function later on.

When there is hardware multiply support, it is more efficient to perform
widening multiplication using the hardware multiplier instead of letting
GCC widen the arguments before calling the multiplication routine in the
wider mode.

gcc/ChangeLog:

	* config/msp430/msp430.md (mulhi3): New.
	(mulsi3): New.
	(mulsidi3): Rename to *mulsidi3_inline.
	(umulsidi3): Rename to *umulsidi3_inline.
	(mulsidi3): New define_expand.
	(umulsidi3): New define_expand.