[8/11][POC][Clang][RISCV] Define tuple type variant of vloxseg2ei32 vluxseg2ei32

For the cover letter of this patch-set, please checkout D146872.

Depends on D147913.

This is the 8th patch of the patch-set.

This patch is a proof-of-concept and will be extended to full coverage
in the future. Currently, the old non-tuple indexed segment load is
not removed, and only signed integer indexed segment load of NF=2,
EEW=32 is defined here.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D147914