[RISCV][Clang] Add all RVV Mask intrinsic functions.

1. Redefine vpopc and vfirst IR intrinsic so it could adapt on
clang tablegen generator which always appends a type for vl
in IntrinsicType of clang codegen.
2. Remove `c` type transformer and add `u` and `l` for unsigned long
and long type.

Authored-by: Roger Ferrer Ibanez <rofirrim@gmail.com>
Co-Authored-by: Zakk Chen <zakk.chen@sifive.com>

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D100120