RISC-V: Add RVV shift.vx C/C++ API support

RISC-V: Add RVV shift.vx C/C++ API support

gcc/ChangeLog:

	* config/riscv/predicates.md (pmode_reg_or_uimm5_operand): New predicate.
	* config/riscv/riscv-vector-builtins-bases.cc: New class.
	* config/riscv/riscv-vector-builtins-functions.def (vsll): Ditto.
	(vsra): Ditto.
	(vsrl): Ditto.
	* config/riscv/riscv-vector-builtins.cc: Ditto.
	* config/riscv/vector.md (@pred_<optab><mode>_scalar): New pattern.