[RISCV] Add patterns for vnsr[a,l].wx where shift amount has different type than...

[RISCV] Add patterns for vnsr[a,l].wx where shift amount has different type than vector element

We're currently only matching scalar shift amounts where the type is the same
as the vector element type. But because only the bottom log2(2*SEW) bits are
used, only 7 bits will be used at most so we can use any scalar type >= i8.

This patch adds patterns for the case above, as well as for when the shift
amount type is the same as the widened element type and doesn't need extended.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D155698