RISC-V: Add min/max patterns for ifcvt.

RISC-V: Add min/max patterns for ifcvt.

ifcvt likes to emit

(set
  (if_then_else)
    (ge (reg 1) (reg2))
    (reg 1)
    (reg 2))

which can be recognized as min/max patterns in the backend.
This patch adds such patterns and the respective iterators as well as a
test.

gcc/ChangeLog:

	* config/riscv/bitmanip.md (*<bitmanip_minmax_cmp_insn>_cmp_<mode>3):
	New min/max ifcvt pattern.
	* config/riscv/iterators.md (minu): New iterator.
	* config/riscv/riscv.cc (riscv_noce_conversion_profitable_p):
	Remove riscv-specific adjustment.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/zbb-min-max-04.c: New test.