[RISCV] Add test cases that show that we're too aggressive about using greviw/gorciw...

[RISCV] Add test cases that show that we're too aggressive about using greviw/gorciw. NFC

We currently type legalize to the W form, but type legalization
doesn't place any requirements on the extended bits. So we are ok
to use GREVI/GORCI for type legalization as long as the control
doesn't cross any bits from the extended bits into the lower bits.

This can allow us to recognize cases where the extended bits end
up being all zeros and we can propagate that information through.

My plan is to move greviw/gorciw formation to isel patterns similar
to slliw.