VAX: Fix predicates and constraints for EXTV/EXTZV/INSV insns

VAX: Fix predicates and constraints for EXTV/EXTZV/INSV insns

It makes no sense for insn operand predicates, as long as they accept a
register operand, to be more restrictive than the set of the associated
constraints, because expand will choose the insn based on the relevant
operand being a pseudo register then and reload keep it happily as a
memory reference if a constraint permits it.  So the restriction posed
by such a predicate will be happily ignored, and moreover if a splitter
is added, such as required for MODE_CC support, the new instructions
will reject the original operands supplied, causing an ICE.  An actual
example will be given with a subsequent change.

Remove such inconsistencies we have with the EXTV/EXTZV/INSV insns then,
observing that a bit-field located in memory is byte-addressed by the
respective machine instructions and therefore SImode may only be used
with a register or an offsettable memory operand (i.e. not an indexed,
pre-decremented, or post-incremented one), which has already been taken
into account with the constraints currently used, except for `*insv_2'.
The QI machine mode may be used for the bit-field location with any kind
of memory operand, but we got the constraint wrong, although harmlessly
in reality, with `*insv'.  Fix that for consistency though.

Also give the insns names, for easier reference here and elsewhere.

	gcc/
	* config/vax/vax.md (*insv_aligned, *extzv_aligned)
	(*extv_aligned, *extv_non_const, *extzv_non_const): Name insns.
	Fix location predicate.
	(*extzv): Name insn.
	(*insv): Likewise.  Fix location constraint.
	(*insv_2): Likewise, and the predicate.