[RISCV] Strength reduce mul by 2^n + 2/4/8 + 1 (#88911)

With zba, we can expand this to (add (shl X, C1), (shXadd X, X)).

Note that this is our first expansion to a three instruction sequence. I
believe this to general be a reasonable tradeoff for most architectures,
but we may want to (someday) consider a tuning flag here.

I plan to support 2^n + (2/4/8 + 1) eventually as well, but that comes
behind 2^N - 2^M. Both are also three instruction sequences.

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Co-authored-by: Min-Yih Hsu <min@myhsu.dev>