Remove global variable arm_linux_vfp_register_count in arm-linux-nat.c

Remove global variable arm_linux_vfp_register_count in arm-linux-nat.c

This patch is to remove the global variable arm_linux_vfp_register_count
from arm-linux-nat.c.  This global variable is set when native gdb
looks for the right target description according HWCAP.  However,
'struct gdbarch_tdep' has already had a field have_vfp_registers, which
is a boolean about whether target has vfp registers or not.  This
patch converts this boolean field to a numeric counter to replace
global variable arm_linux_vfp_register_count.

gdb:

2015-05-28  Yao Qi  <yao.qi@linaro.org>

	* arm-linux-nat.c (arm_linux_vfp_register_count): Remove.
	(fetch_vfp_regs): Use vfp_register_count from gdbarch_tdep
	instead of arm_linux_vfp_register_count.
	(store_vfp_regs): Likewise.
	(arm_linux_fetch_inferior_registers): Likewise.
	(arm_linux_store_inferior_registers): Likewise.
	(arm_linux_read_description): Don't set
	arm_linux_vfp_register_count.
	* arm-linux-tdep.c (arm_linux_iterate_over_regset_sections):
	Adjust.
	* arm-tdep.c (arm_gdbarch_init): Add assert on
	vfp_register_count.
	* arm-tdep.h (struct gdbarch_tdep) <have_vfp_registers>: Rename
	field to vfp_register_count.  All users updated.