Support Z0 packet in AArch64 multi-arch debugging

Support Z0 packet in AArch64 multi-arch debugging

In commit 6085d6f6, Z0 packet is disabled in aarch64 GDBserver if
the inferior is 32-bit or there may be multiple inferiors, because
Z0 packet isn't supported for arm then.  Recently, Z0 packet
is supported in arm target, so we don't have such limitation in
aarch64 GDBserver, that is to say, aarch64 GDBserver can use Z0
packet in multi-arch/multi-inferior debugging when the inferior's
arch is arm.

Part of this patch is to revert 6085d6f6, and the rest of the patch
is to move some breakpoint related arm_* functions into
linux-aarch32-low.c in order to share them between arm and aarch64.

This patch is regression tested on aarch64-linux for debugging both
aarch64 programs and arm programs respectively.

gdb/gdbserver:

2015-12-07  Yao Qi  <yao.qi@linaro.org>

	* configure.srv: Append arm.o to srv_tgtobj for
	aarch64*-*-linux* target.
	* linux-aarch32-low.c (arm_abi_breakpoint): New macro.  Moved
	from linux-arm-low.c.
	(arm_eabi_breakpoint, arm_breakpoint): Likewise.
	(arm_breakpoint_len, thumb_breakpoint): Likewise.
	(thumb_breakpoint_len, thumb2_breakpoint): Likewise.
	(thumb2_breakpoint_len): Likewise.
	(arm_is_thumb_mode, arm_breakpoint_at): Likewise.
	(arm_breakpoint_kinds): Likewise.
	(arm_breakpoint_kind_from_pc): Likewise.
	(arm_sw_breakpoint_from_kind): Likewise.
	(arm_breakpoint_kind_from_current_state): Likewise.
	* linux-aarch32-low.h (arm_breakpoint_kind_from_pc): Declare.
	(arm_sw_breakpoint_from_kind): Declare.
	(arm_breakpoint_kind_from_current_state): Declare.
	(arm_breakpoint_at): Declare.
	* linux-aarch64-low.c (aarch64_sw_breakpoint_from_kind): Call
	arm_sw_breakpoint_from_kind if process is 32-bit.
	(aarch64_breakpoint_kind_from_pc): New function.
	(aarch64_breakpoint_kind_from_current_state): New function.
	(the_low_target): Initialize fields breakpoint_kind_from_pc
	and breakpoint_kind_from_current_state.
	* linux-arm-low.c (arm_breakpoint_kinds): Move to
	linux-aarch32-low.c.
	(arm_abi_breakpoint, arm_eabi_breakpoint): Likewise.
	(arm_breakpoint, arm_breakpoint_len): Likewise.
	(thumb_breakpoint, thumb_breakpoint_len): Likewise.
	(thumb2_breakpoint, thumb2_breakpoint_len): Likewise.
	(arm_is_thumb_mode): Likewise.
	(arm_breakpoint_at): Likewise.
	(arm_breakpoint_kind_from_pc): Likewise.
	(arm_sw_breakpoint_from_kind): Likewise.
	(arm_breakpoint_kind_from_current_state): Likewise.

	Revert:
	2015-08-04  Yao Qi  <yao.qi@linaro.org>

	* linux-aarch64-low.c (aarch64_supports_z_point_type): Return
	0 for Z_PACKET_SW_BP if it may be used in multi-arch debugging.
	* server.c (extended_protocol): Remove "static".
	* server.h (extended_protocol): Declare it.