[4/11][Clang][RISCV] Expand all variants for unit stride segment store

This is the 4th patch of the patch-set. For the cover letter, please
checkout D152069.

Depends on D152071.

This patch expands all variants for unit stride segment store. The
store intrinsics does not have any 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
vsseg2e32 is added.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D152072