[RISCV] Add missing CHECKs to vector test

Since the "LMUL-MAX=2" output for some test functions differed between
RV32 and RV64, the update_llc_test_checks script failed to emit a
unified LMULMAX2 check for them. I'm not sure why it didn't warn about
this.

This patch also takes the opportunity to add unified RV32/RV64 checks to
help shorten the test file when the output for LMULMAX1 and LMULMAX2 is
identical but differs between the two ISAs.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D98944