[10/11][POC][Clang][RISCV] Define vget for tuple type

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

Depends on D147915.

This is the 10th patch of the patch-set.

This patch is a proof-of-concept and will be extended to full coverage
in the future. Only vget for tuple type of NF=2, EEW=32, LMUL=1 is
defined now.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D147916