ARM: fix typo in VFP instruction definition

The vstm family of VFP instructions belong to the VFP store itinerary class, not
the VFP load itinerary class.
ARM: fix a few typos in comments
ARM: provide VFP aliases for pre-V6 mnemonics

In order to provide compatibility with the GNU assembler, provide aliases for
pre-UAL mnemonics for floating point operations.