Implement breakpoint_kind_from_pc and sw_breakpoint_from_kind for ARM in GDBServer.

Implement breakpoint_kind_from_pc and sw_breakpoint_from_kind for ARM in GDBServer.

ARM can have multiple breakpoint types based on the instruction set
it's currently in: arm, thumb or thumb2.

GDBServer needs to know what breakpoint is to be inserted at location
when inserting a breakpoint.

This is handled by the breakpoint_kind_from_pc and sw_breakpoint_from_kind
target ops introduced in a previous patch, this patch adds the
arm_breakpoint_kind_from_pc and arm_sw_breakpoint_from_kind implementation so
that the proper breakpoint type is returned based on the pc.

Also in order to share some code with GDB a new file called arm.c have been
introduced in arch/.

While this file does not contain much yet future patches will add more
to it thus the inclusion at this stage.

No regressions on Ubuntu 14.04 on ARMv7 and x86.
With gdbserver-{native,extended} / { -marm -mthumb }

gdb/ChangeLog:

	* Makefile.in: Add arm.c/o.
	* arch/arm.c: New file.
	* arch/arm.h: (IS_THUMB_ADDR): Move macro from arm-tdep.c.
	(MAKE_THUMB_ADDR): Likewise.
	(UNMAKE_THUMB_ADDR): Likewise.
	* arm-tdep.c (int thumb_insn_size): Move to arm.c.
	(IS_THUMB_ADDR): Move to arm.h.
	(MAKE_THUMB_ADDR): Likewise.
	(UNMAKE_THUMB_ADDR): Likewise.
	* configure.tgt: Add arm.o to all ARM configs.

gdb/gdbserver/ChangeLog:

	* Makefile.in: Add arm.c/o.
	* configure.srv: Likewise.
	* linux-arm-low.c (arm_breakpoint_kinds): New enum.
	(arm_breakpoint_kind_from_pc): New function.
	(arm_sw_breakpoint_from_kind): Return proper kind.
	(struct linux_target_ops) <breakpoint_kind_from_pc>: Initialize.