[RISCV][NFC] Increase test coverage of Zbt extension

[RISCV][NFC] Increase test coverage of Zbt extension

Add Zbt (ternary) extension code generation to the select lowering
tests since it can have a significant impact on how select is
lowered.

While we are here make the neg-abs commands more consistent with
the other tests.

Reviewed By: lenary

Differential Revision: https://reviews.llvm.org/D94798