[6/11][POC][Clang][RISCV] Define tuple type variant of vlsseg2e32

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

Depends on D147911.

This is the 6th 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 strided segment load is not
removed, and only signed integer strided segment load of NF=2, EEW=32
is defined here.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D147912