[8/11][Clang][RISCV] Expand all variants for indexed strided segment load

This is the 8th patch of the patch-set. For the cover letter, please
checkout D152069.

Depends on D152075.

This patch expands all variants of indexed strided segment load,
including the policy variants. This patch also fixes the trailing suffix
in the intrinsics' function name that representing the return type,
adding `x{NF}`.

For the same reason mentioned in [3/11], only full test case for
vluxseg2ei32, vloxseg2ei32 is added for now.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D152076