[SveEmitter] Add more immediate operand checks.

This patch adds a number of intrinsics that take immediates with
varying ranges based on the element size one of the operands.

    svext:   immediate ranging 0 to (2048/sizeinbits(elt) - 1)
    svasrd:  immediate ranging 1..sizeinbits(elt)
    svqshlu: immediate ranging 1..sizeinbits(elt)/2
    ftmad:   immediate ranging 0..(sizeinbits(elt) - 1)

Reviewers: efriedma, SjoerdMeijer, rovka, rengolin

Reviewed By: SjoerdMeijer

Tags: #clang

Differential Revision: https://reviews.llvm.org/D76679