RISC-V: Recognized Svinval and Svnapot extensions

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc (riscv_ext_version_table):
	Add svinval and svnapot extension.
	(riscv_ext_flag_table): Ditto.
	* config/riscv/riscv-opts.h (MASK_SVINVAL): New.
	(MASK_SVNAPOT): Ditto.
	(TARGET_SVINVAL): Ditto.
	(TARGET_SVNAPOT): Ditto.
	* config/riscv/riscv.opt (riscv_sv_subext): New.

gcc/testsuite/ChangeLog:
	* gcc.target/riscv/predef-24.c:New.
	* gcc.target/riscv/predef-25.c:New.