RISC-V: Add zhinx/zhinxmin testcases.

RISC-V: Add zhinx/zhinxmin testcases.

Test zhinx/zhinxmin support, same like with zfh/zfhmin testcases
but use gprs and don't use fmv instruction.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/_Float16-zhinx-1.c: New test.
	* gcc.target/riscv/_Float16-zhinx-2.c: New test.
	* gcc.target/riscv/_Float16-zhinx-3.c: New test.
	* gcc.target/riscv/_Float16-zhinxmin-1.c: New test.
	* gcc.target/riscv/_Float16-zhinxmin-2.c: New test.
	* gcc.target/riscv/_Float16-zhinxmin-3.c: New test.