RISC-V: Reorganize and rename combine patterns in autovec-opt.md

RISC-V: Reorganize and rename combine patterns in autovec-opt.md

This patch reorganize and rename the combine patterns in autovec-opt.md
by category. There shouldn't be any functional changes.
The current classification includes the following categories:

- Combine op + vmerge to cond_op
- Combine binop + trunc to narrow_binop
- Combine extend + binop to widen_binop
- Combine extend + ternop to widen_ternop
- Misc combine patterns

gcc/ChangeLog:

	* config/riscv/autovec-opt.md (*<optab>not<mode>): Move and rename.
	(*n<optab><mode>): Ditto.
	(*v<any_shiftrt:optab><any_extend:optab>trunc<mode>): Ditto.
	(*<any_shiftrt:optab>trunc<mode>): Ditto.
	(*narrow_<any_shiftrt:optab><any_extend:optab><mode>): Ditto.
	(*narrow_<any_shiftrt:optab><mode>_scalar): Ditto.
	(*single_widen_mult<any_extend:su><mode>): Ditto.
	(*single_widen_mul<any_extend:su><mode>): Ditto.
	(*single_widen_mult<mode>): Ditto.
	(*single_widen_mul<mode>): Ditto.
	(*dual_widen_fma<mode>): Ditto.
	(*dual_widen_fma<su><mode>): Ditto.
	(*single_widen_fma<mode>): Ditto.
	(*single_widen_fma<su><mode>): Ditto.
	(*dual_fma<mode>): Ditto.
	(*single_fma<mode>): Ditto.
	(*dual_fnma<mode>): Ditto.
	(*dual_widen_fnma<mode>): Ditto.
	(*single_fnma<mode>): Ditto.
	(*single_widen_fnma<mode>): Ditto.
	(*dual_fms<mode>): Ditto.
	(*dual_widen_fms<mode>): Ditto.
	(*single_fms<mode>): Ditto.
	(*single_widen_fms<mode>): Ditto.
	(*dual_fnms<mode>): Ditto.
	(*dual_widen_fnms<mode>): Ditto.
	(*single_fnms<mode>): Ditto.
	(*single_widen_fnms<mode>): Ditto.