Add widening expansion of MULT_HIGHPART_EXPR for integral modes

Add widening expansion of MULT_HIGHPART_EXPR for integral modes

For integral modes the expansion of MULT_HIGHPART_EXPR requires the presence
of an {s,u}mul_highpart optab whereas, for vector modes, widening expansion
is supported.  This adds a widening expansion for integral modes too, which
is in fact already implemented in expmed_mult_highpart_optab.

gcc/
	* expmed.h (expmed_mult_highpart_optab): Declare.
	* expmed.cc (expmed_mult_highpart_optab): Remove static keyword.
	Do not assume that OP1 is a constant integer.  Fix pasto.
	(expmed_mult_highpart): Pass OP1 narrowed to MODE in all the calls
	to expmed_mult_highpart_optab.
	* optabs-query.cc (can_mult_highpart_p): Use 2 for integer widening
	and shift subsequent values accordingly.
	* optabs.cc (expand_mult_highpart): Call expmed_mult_highpart_optab
	when can_mult_highpart_p returns 2 and adjust to above change.