Add Arm to the list of feature target description targets and generate the
relevant C files.
Add arm-m-profile-with-fpa.xml as the feature version of the exisiting
arm-with-m-fpa-layout.xml.
Add extra comments to the Makefile for readability.
New files are not yet used.
gdb/ChangeLog:
* features/Makefile: Use feature target descriptions for Arm.
* features/arm/arm-core.c: Generate new file.
* features/arm/arm-fpa.c: Likewise.
* features/arm/arm-m-profile-with-fpa.xml: Likewise.
* features/arm/arm-m-profile.c: Likewise.
* features/arm/arm-vfpv2.c: Likewise.
* features/arm/arm-vfpv3.c: Likewise.
* features/arm/xscale-iwmmxt.c: Likewise.
* target-descriptions.c (maint_print_c_tdesc_cmd): Add Arm.
