[SVE] Optimize new cases for lowerConvertToSVBool

Converts to SVBool are already considered as a nop, if they
are converting an operand from a ptrue or a cmp, because
they zero the extra predicate lanes by construction.

This patch adds 2 similar cases:
- The wide cmp, which were not directly recognized by the test
for other forms of cmp
- Splats of 1, which will be generated as ptrue, and as such
will also zero the extra predicate lines.

Reviewed By: paulwalker-arm, peterwaller-arm

Differential Revision: https://reviews.llvm.org/D124908