Don't use arm_regmap and arm_num_regs in arm_fill_gregset and arm_store_gregset

Don't use arm_regmap and arm_num_regs in arm_fill_gregset and arm_store_gregset

In order to align with arm-linux-nat.c counterparts, we don't use
arm_num_regs and arm_regmap in functions arm_fill_gregset and
arm_store_gregset.  Instead, we use register numbers.  With this
patch applied, arm_fill_gregset and arm_store_gregset don't need
arm_num_regs and arm_regmap, and they will be moved to a separate
file shared for both arm and aarch64 in the following patch.

gdb/gdbserver:

2015-07-30  Yao Qi  <yao.qi@linaro.org>

	* linux-arm-low.c: Include arch/arm.h.
	(arm_fill_gregset): Don't use arm_num_regs and arm_regmap.
	(arm_store_gregset): Likewise.