RISC-V: Removed privileged spec 1.9.1 support in assembler.

RISC-V: Removed privileged spec 1.9.1 support in assembler.

Removed since it's may have lots of conflicts with the newer extensions, but
still keep linker recognizes it in case of linking old objects.

gas/
	* NEWS: Updated.
	* config/tc-riscv.c (riscv_set_default_priv_spec): Regard 1.9.1 as
	an unknown version.
	(md_show_usage): Removed privileged spec 1.9.1 information.
	* testsuite/gas/riscv/attribute-05.s: Updated since privileged spec
	1.9.1 is unsupported.
	* testsuite/gas/riscv/attribute-05.d: Likewise.
	* testsuite/gas/riscv/attribute-12.d: Likewise.
	* testsuite/gas/riscv/attribute-13.d: Likewise.
	* testsuite/gas/riscv/csr-dw-regnums.d: Likewise.
	* testsuite/gas/riscv/csr-dw-regnums.s: Likewise.
	* testsuite/gas/riscv/csr.s: Likewise.
	* testsuite/gas/riscv/csr-version-1p10.d: Likewise.
	* testsuite/gas/riscv/csr-version-1p10.l: Likewise.
	* testsuite/gas/riscv/csr-version-1p11.d: Likewise.
	* testsuite/gas/riscv/csr-version-1p11.l: Likewise.
	* testsuite/gas/riscv/csr-version-1p12.d: Likewise.
	* testsuite/gas/riscv/csr-version-1p12.l: Likewise.
	* testsuite/gas/riscv/csr-version-1p9p1.d: Removed.
	* testsuite/gas/riscv/csr-version-1p9p1.l: Removed.
include/
	* opcode/riscv-opc.h: Updated since privileged spec 1.9.1 is
	unsupported.
ld/
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-01.d: Updated since
	privileged spec 1.9.1 is unsupported.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-02.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-03.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-a.s: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-b.s: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-01.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-02.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-03.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-04.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-05.d: Likewise.
	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-06.d: Likewise.