[RISCV][test] Add new tests for mul optimization in the zba extension with SH*ADD

This patch will show the following optimization by future patches.

(mul x imm) -> (SH1ADD x, (SLLI x, bits)) when imm = 2^n + 2.
(mul x imm) -> (SH2ADD x, (SLLI x, bits)) when imm = 2^n + 4.
(mul x imm) -> (SH3ADD x, (SLLI x, bits)) when imm = 2^n + 8.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D105614