[RISCV][test] Add new tests of SH*ADD in the zba extension
These tests will show the following optimization by future patches.
Rx + Ry * 6 => (SH1ADD (SH2ADD Rx, Ry), Ry)
Rx + Ry * 10 => (SH1ADD (SH3ADD Rx, Ry), Ry)
Rx + Ry * 12 => (SH2ADD (SH3ADD Rx, Ry), Ry)
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D104210