[arm] Allow new extended syntax CPU and architecture

This patch extends support for the new extended-style architecture
strings to configure and the target default options.  We validate any
options passed by the user to configure against the permitted
extensions for that CPU or architecture.

	* config.gcc (arm*-*-fucshia*): Set target_cpu_cname to the real
	cpu name.
	(arm*-*-*): Set target_cpu_default2 to a quoted string.
	* config/arm/parsecpu.awk (check_cpu): Validate any extension
	options.
	(check_arch): Likewise.
	* config/arm/arm.c (arm_configure_build_target): Handle
	TARGET_CPU_DEFAULT being a string constant.  Scan any feature
	options in the default.

From-SVN: r249290