[RISCV] Add CodeGen support and MC testcase of RISCV Zca Extension

This patch add the support of RISCV Zca ext

`Zca` is a subset of C extension instructions that are compatible with the Zc extension.

So this patch implements Zca code generation with reference to the C extension and sets the 2-byte alignment for the Zca extension, just like C extension does.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D130483