[AArch64] Rework ARMv8.1 command line options.

[AArch64] Rework ARMv8.1 command line options.

	* config/aarch64/aarch64-options-extensions.def: Remove
	AARCH64_FL_RDMA from "fp" and "simd".  Remove "pan", "lor",
	"rdma".
	* config/aarch64/aarch64.h (AARCH64_FL_PAN): Remove.
	(AARCH64_FL_LOR): Remove.
	(AARCH64_FL_RDMA): Remove.
	(AARCH64_FL_V8_1): New.
	(AARCH64_FL_FOR_AARCH8_1): Replace AARCH64_FL_PAN, AARCH64_FL_LOR
	and AARCH64_FL_RDMA with AARCH64_FL_V8_1.
	(AARCH64_ISA_RDMA): Replace AARCH64_FL_RDMA with AARCH64_FL_V8_1.
	* doc/invoke.texi (AArch64 -march): Rewrite initial paragraph and
	section on -march=native.  Group descriptions of permitted
	architecture names together.  Expand description of
	-march=armv8.1-a.
	(AArch64 -mtune): Slightly rework section on -march=native.
	(AArch64 -mcpu): Slightly rework section on -march=native.
	(AArch64 Feature Modifiers): Remove "pan", "lor" and "rdma".
	State that -march=armv8.1-a enables "crc" and "lse".

From-SVN: r231400