Fix breakpoint size when stepping over a permanent breakpoint in GDBServer.

Fix breakpoint size when stepping over a permanent breakpoint in GDBServer.

When manually stepping over a permanent breakpoint on ARM we need to fetch the
right breakpoint size based on the current instruction set used.

Since this is not encoded in the stop_pc, the instruction mode needs to be
fetched from the CPSR register.

This is done by introducing a new target operation called :
breakpoint_kind_from_current_state.

For other targets that do not need this, breakpoint_kind_from_pc is used.

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

gdb/gdbserver/ChangeLog:

	* linux-arm-low.c (arm_is_thumb_mode): New function.
	(arm_breakpoint_at): Use arm_is_thumb_mode.
	(arm_breakpoint_kind_from_current_state): New function.
	(struct linux_target_ops) <breakpoint_kind_from_current_state>:
	Initialize.
	* linux-low.c (linux_wait_1): Call breakpoint_kind_from_current_state.
	(linux_breakpoint_kind_from_current_state): New function.
	(struct target_ops <breakpoint_kind_from_current_state>: Initialize.
	* linux-low.h (struct linux_target_ops)
	<breakpoint_kind_from_current_state>: New field.
	* target.h (struct target_ops): Likewise.
	(target_breakpoint_kind_from_current_state): New macro.