[RISCV] Optimize mul in the zba extension with SH*ADD

This patch makes the following optimization, if the
immediate multiplier is not a simm12.

(mul x, (power_of_2 + 2)) => (SH1ADD x, (SLLI x, bits))
(mul x, (power_of_2 + 4)) => (SH2ADD x, (SLLI x, bits))
(mul x, (power_of_2 + 8)) => (SH3ADD x, (SLLI x, bits))

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D106648