[6/11][Clang][RISCV] Expand all variants for strided segment load

This is the 6th patch of the patch-set. For the cover letter, please
checkout D152069.

Depends on D152073.

This patch expands all variants of 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
vlsseg2e32 is added.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D152074