Arm: Use feature target descriptions

Arm: Use feature target descriptions

In arm arm_create_target_description and
aarch32_create_target_description create feature based target descriptions
instead of returning the old style descriptions.

Ensure the descriptions are created in exactly the same way as the old xml
files.

Remove the old initialize calls.

gdb/ChangeLog:

	* arch/aarch32.c (aarch32_create_target_description): Create
	target descriptions using features.
	* arch/arm.c (arm_create_target_description)
	(arm_create_mprofile_target_description): Likewise.
	* arm-tdep.c (_initialize_arm_tdep): Remove tdesc init calls.