RISC-V: Add autovect widening/narrowing Integer/FP conversions.

RISC-V: Add autovect widening/narrowing Integer/FP conversions.

This patch implements widening and narrowing float-to-int and
int-to-float conversions and adds tests.

gcc/ChangeLog:

	* config/riscv/autovec.md (<optab><vnconvert><mode>2): New
	expander.
	(<float_cvt><vnconvert><mode>2): Ditto.
	(<optab><mode><vnconvert>2): Ditto.
	(<float_cvt><mode><vnconvert>2): Ditto.
	* config/riscv/vector-iterators.md: Add vnconvert.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/conversions/vfncvt-ftoi-run.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfncvt-ftoi-rv32gcv.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfncvt-ftoi-rv64gcv.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfncvt-ftoi-template.h: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfncvt-ftoi-zvfh-run.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfncvt-itof-run.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfncvt-itof-rv32gcv.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfncvt-itof-rv64gcv.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfncvt-itof-template.h: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfncvt-itof-zvfh-run.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfwcvt-ftoi-run.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfwcvt-ftoi-rv32gcv.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfwcvt-ftoi-rv64gcv.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfwcvt-ftoi-template.h: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfwcvt-ftoi-zvfh-run.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfwcvt-itof-run.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfwcvt-itof-rv32gcv.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfwcvt-itof-rv64gcv.c: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfwcvt-itof-template.h: New test.
	* gcc.target/riscv/rvv/autovec/conversions/vfwcvt-itof-zvfh-run.c: New test.