[arm] Add a few missing architecture extension options.

[arm] Add a few missing architecture extension options.

Reviewing the list of options for the purposes of writing the
documentation revealed that a small number of options were missing.
Mostly these are aliases for existing options, but in a couple of
cases we lacked the ability to disable certain other options.

	* config/arm/arm-cpus.in (armv7): Add extension +nofp.
	(armv7-r): Add aliases vfpv3xd and vfpv3-d16.
	(armv8-m.main): Add option +nodsp.
	* config/arm/arm-cpu-cdata.h: Regenerated.

From-SVN: r249306