[globalisel] Add support for ValueType operands in patterns.

It's rare but there are a small number of patterns like this:
    (set i64:$dst, (add i64:$src1, i64:$src2))
These should be equivalent to register classes except they shouldn't check for
a specific register bank.

This doesn't occur in AArch64/ARM/X86 but does occasionally come up in other
in-tree targets such as BPF.

llvm-svn: 315226