RISC-V: Add RVV registers register spilling

RISC-V: Add RVV registers register spilling

This patch support RVV scalable register spilling.
prologue && epilogue handling pick up prototype from Monk Chiang <monk.chiang@sifive.com>.
Co-authored-by: Monk Chiang <monk.chiang@sifive.com>
gcc/ChangeLog:

	* config/riscv/riscv-v.cc (emit_pred_move): Adjust for scalable register spilling.
	(legitimize_move): Ditto.
	* config/riscv/riscv.cc (riscv_v_adjust_scalable_frame): New function.
	(riscv_first_stack_step): Adjust for scalable register spilling.
	(riscv_expand_prologue): Ditto.
	(riscv_expand_epilogue): Ditto.
	(riscv_dwarf_poly_indeterminate_value): New function.
	(TARGET_DWARF_POLY_INDETERMINATE_VALUE): New target hook support for register spilling.
	* config/riscv/riscv.h (RISCV_DWARF_VLENB): New macro.
	(RISCV_PROLOGUE_TEMP2_REGNUM): Ditto.
	(RISCV_PROLOGUE_TEMP2): Ditto.
	* config/riscv/vector-iterators.md: New iterators.
	* config/riscv/vector.md (*mov<mode>): Fix it for register spilling.
	(*mov<mode>_whole): New pattern.
	(*mov<mode>_fract): New pattern.
	(@pred_mov<mode>): Fix it for register spilling.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/macro.h: New test.
	* gcc.target/riscv/rvv/base/spill-1.c: New test.
	* gcc.target/riscv/rvv/base/spill-10.c: New test.
	* gcc.target/riscv/rvv/base/spill-11.c: New test.
	* gcc.target/riscv/rvv/base/spill-12.c: New test.
	* gcc.target/riscv/rvv/base/spill-2.c: New test.
	* gcc.target/riscv/rvv/base/spill-3.c: New test.
	* gcc.target/riscv/rvv/base/spill-4.c: New test.
	* gcc.target/riscv/rvv/base/spill-5.c: New test.
	* gcc.target/riscv/rvv/base/spill-6.c: New test.
	* gcc.target/riscv/rvv/base/spill-7.c: New test.
	* gcc.target/riscv/rvv/base/spill-8.c: New test.
	* gcc.target/riscv/rvv/base/spill-9.c: New test.