Replace some $ARCH_{get,set}_pc with linux_{get,set}_pc_32bit

Replace some $ARCH_{get,set}_pc with linux_{get,set}_pc_32bit

This patch adds a pair of new functions linux_get_pc_32bit and
linux_set_pc_32bit which get and set 32-bit register "pc" from
regcache.  This function can be used some targets and these own
$ARCH_{get,set}_pc are replaced by linux_{get,set}_pc_32bit
respectively.

This patch touches many targets, but I only have arm board to
test and no regression.  I also rebuilt nios2-linux GDBserver.
If it is right to go, I'll post the 64-bit counterpart later.

gdb/gdbserver:

2016-01-18  Yao Qi  <yao.qi@linaro.org>

	* linux-arm-low.c (debug_threads): Remove declaration.
	(arm_get_pc, arm_set_pc): Remove.
	(the_low_target): Use linux_get_pc_32bit and
	linux_set_pc_32bit.
	* linux-bfin-low.c (bfin_get_pc, bfin_set_pc): Remove.
	(the_low_target): Use linux_get_pc_32bit and
	linux_set_pc_32bit.
	* linux-cris-low.c (debug_threads): Remove declaration.
	(cris_get_pc, cris_set_pc,): Remove.
	(the_low_target): Use linux_get_pc_32bit and
	linux_set_pc_32bit.
	* linux-crisv32-low.c (debug_threads): Remove declaration.
	(cris_get_pc, cris_set_pc): Remove.
	(the_low_target): Use linux_get_pc_32bit and
	linux_set_pc_32bit.
	* linux-low.c: Include inttypes.h.
	(linux_get_pc_32bit, linux_set_pc_32bit): New functions.
	* linux-low.h (linux_get_pc_32bit, linux_set_pc_32bit): Declare.
	* linux-m32r-low.c (m32r_get_pc, m32r_set_pc): Remove.
	(the_low_target): Use linux_get_pc_32bit and
	linux_set_pc_32bit.
	* linux-m68k-low.c (m68k_get_pc, m68k_set_pc): Remove.
	(the_low_target): Use linux_get_pc_32bit and
	linux_set_pc_32bit.
	* linux-nios2-low.c (nios2_get_pc, nios2_set_pc): Remove.
	(the_low_target): Use linux_get_pc_32bit and
	linux_set_pc_32bit.
	* linux-sh-low.c (sh_get_pc, sh_set_pc): Remove.
	(the_low_target): Use linux_get_pc_32bit and
	linux_set_pc_32bit.
	* linux-xtensa-low.c (xtensa_get_pc, xtensa_set_pc): Remove.
	(the_low_target): Use linux_get_pc_32bit and
	linux_set_pc_32bit.