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

These tests will show the following optimization by future patches.

(mul x, 11) -> (SH1ADD (SH2ADD x, x), x)
(mul x, 19) -> (SH1ADD (SH3ADD x, x), x)
(mul x, 13) -> (SH2ADD (SH1ADD x, x), x)
(mul x, 21) -> (SH2ADD (SH2ADD x, x), x)
(mul x, 37) -> (SH2ADD (SH3ADD x, x), x)
(mul x, 25) -> (SH3ADD (SH1ADD x, x), x)
(mul x, 41) -> (SH3ADD (SH2ADD x, x), x)
(mul x, 73) -> (SH3ADD (SH3ADD x, x), x)

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D106031