Move instruction decoding into new arch/ directory

Move instruction decoding into new arch/ directory

This patch moves the following functions into the arch/ common
directory, in new files arch/aarch64-insn.{h,c}.  They are prefixed with
'aarch64_':

 - aarch64_decode_adrp
 - aarch64_decode_b
 - aarch64_decode_cb
 - aarch64_decode_tb

We will need them to implement fast tracepoints in GDBserver.

For consistency, this patch also adds the 'aarch64_' prefix to static
decoding functions that do not need to be shared right now.

V2:
 make sure the formatting issues propagated
 fix `gdbserver/configure.srv'.

gdb/ChangeLog:

	* Makefile.in (ALL_64_TARGET_OBS): Add aarch64-insn.o.
	(HFILES_NO_SRCDIR): Add arch/aarch64-insn.h.
	(aarch64-insn.o): New rule.
	* configure.tgt (aarch64*-*-elf): Add aarch64-insn.o.
	(aarch64*-*-linux*): Likewise.
	* arch/aarch64-insn.c: New file.
	* arch/aarch64-insn.h: New file.
	* aarch64-tdep.c: Include arch/aarch64-insn.h.
	(aarch64_debug): Move to arch/aarch64-insn.c.  Declare in
	arch/aarch64-insn.h.
	(decode_add_sub_imm): Rename to ...
	(aarch64_decode_add_sub_imm): ... this.
	(decode_adrp): Rename to ...
	(aarch64_decode_adrp): ... this.  Move to arch/aarch64-insn.c.
	Declare in arch/aarch64-insn.h.
	(decode_b): Rename to ...
	(aarch64_decode_b): ... this.  Move to arch/aarch64-insn.c.
	Declare in arch/aarch64-insn.h.
	(decode_bcond): Rename to ...
	(aarch64_decode_bcond): ... this.  Move to arch/aarch64-insn.c.
	Declare in arch/aarch64-insn.h.
	(decode_br): Rename to ...
	(aarch64_decode_br): ... this.
	(decode_cb): Rename to ...
	(aarch64_decode_cb): ... this.  Move to arch/aarch64-insn.c.
	Declare in arch/aarch64-insn.h.
	(decode_eret): Rename to ...
	(aarch64_decode_eret): ... this.
	(decode_movz): Rename to ...
	(aarch64_decode_movz): ... this.
	(decode_orr_shifted_register_x): Rename to ...
	(aarch64_decode_orr_shifted_register_x): ... this.
	(decode_ret): Rename to ...
	(aarch64_decode_ret): ... this.
	(decode_stp_offset): Rename to ...
	(aarch64_decode_stp_offset): ... this.
	(decode_stp_offset_wb): Rename to ...
	(aarch64_decode_stp_offset_wb): ... this.
	(decode_stur): Rename to ...
	(aarch64_decode_stur): ... this.
	(decode_tb): Rename to ...
	(aarch64_decode_tb): ... this.  Move to arch/aarch64-insn.c.
	Declare in arch/aarch64-insn.h.
	(aarch64_analyze_prologue): Adjust calls to renamed functions.

gdb/gdbserver/ChangeLog:

	* Makefile.in (aarch64-insn.o): New rule.
	* configure.srv (aarch64*-*-linux*): Add aarch64-insn.o.