[RISCV] Add MC support for more P extension instructions. (#153458)
These instructions are the shift by immediate and saturate by immediate
instructions from the top half of page 9 of
https://jhauser.us/RISCV/ext-P/RVP-instrEncodings-015.pdf
I've also improved the CHECK lines in the invalid tests to check line
and column number from the diagnostic.
Co-authored-by: realqhc <caiqihan021@hotmail.com>