[PATCH v3][PR gdb/14383]: gdb: corefile support for arm-none-eabi target

[Fredrik Hederstierna]

This patch adds corefile support for arm-none-eabi targets.

2020-10-20  Fredrik Hederstierna  <fredrik@hederstierna.com>

	PR gdb/14383
	* Makefile.in (ALL_TARGET_OBS): Add new files below.
	* configure.tgt: Add support for none target.
	* arm-tdep.c (arm_gdbarch_init): Added init for default none corefile.
	* arm-none-tdep.h: New file.
	* arm-none-tdep.c: New file.
	* none-tdep.h: New file.
	* none-tdep.c: New file.