RISC-V: Minimal support of bitmanip extension

RISC-V: Minimal support of bitmanip extension

2021-10-25  Kito Cheng  <kito.cheng@sifive.com>

gcc/ChangeLog:

	* common/config/riscv/riscv-common.c (riscv_ext_version_table):
	Add zba, zbb, zbc and zbs.
	(riscv_ext_flag_table): Ditto.
	* config/riscv/riscv-opts.h (MASK_ZBA): New.
	(MASK_ZBB): Ditto.
	(MASK_ZBC): Ditto.
	(MASK_ZBS): Ditto.
	(TARGET_ZBA): Ditto.
	(TARGET_ZBB): Ditto.
	(TARGET_ZBC): Ditto.
	(TARGET_ZBS): Ditto.
	* config/riscv/riscv.opt (riscv_zb_subext): New.