Fetch and store FP registers by PTRACE_{G,S}ETREGSET

Fetch and store FP registers by PTRACE_{G,S}ETREGSET

If kernel supports PTRACE_GETREGSET, GDB uses PTRACE_{G,S}ETREGSET
to fetch and store FP registers.

gdb:

2015-06-01  Yao Qi  <yao.qi@linaro.org>

	* arm-linux-nat.c (fetch_fpregister): Use PTRACE_GETREGSET.
	(fetch_fpregs): Likewise.
	* arm-linux-nat.c (store_fpregister): Use PTRACE_SETREGSET.
	(store_fpregs): Likewise.