gdb/regformats: Don't build .dat files that aren't used by GDBserver

gdb/regformats: Don't build .dat files that aren't used by GDBserver

The only reason .dat files exist is for GBBserver to use them in its
build system.

A few .dat files are listed as targets for generation that shouldn't.
The target descriptions these files are built from aren't used by
GDBserver.  They're fallback descriptions GDB itself has baked in.

Remove them from the list of .dat files to be generated, otherwise a
plain "make" under src/gdb/features/ generates new .dat files that
aren't even in the tree today.

gdb/
2014-10-01  Pedro Alves  <palves@redhat.com>

	* features/Makefile (WHICH): Remove arm-with-m,
	arm-with-m-fpa-layout and arm-with-m-vfp-d16.