[PATCH] RISC-V: Add smcntrpmf extension.

[PATCH] RISC-V: Add smcntrpmf extension.

This patch support smcntrpmf extension[1].
To enable GCC to recognize and process smcntrpmf extension correctly at compile time.

[1]https://github.com/riscvarchive/riscv-smcntrpmf

gcc/ChangeLog:

	* config/riscv/riscv-ext.def: New extension defs.
	* config/riscv/riscv-ext.opt: Ditto.
	* doc/riscv-ext.texi: Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/arch-59.c: New test.