gdbserver: turn target ops 'fetch_registers' and 'store_registers' into methods

gdbserver: turn target ops 'fetch_registers' and 'store_registers' into methods

gdbserver/ChangeLog:
2020-02-20  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	Turn process_stratum_target's fetch_registers and store_registers
	ops into methods of process_target.

	* target.h (struct process_stratum_target): Remove the target ops.
	(class process_target): Add the target ops.
	(fetch_inferior_registers): Update the macro.
	(store_inferior_registers): Update the macro.

	Update the derived classes and callers below.

	* linux-low.cc (linux_target_ops): Update.
	(linux_fetch_registers): Turn into ...
	(linux_process_target::fetch_registers): ... this.
	(linux_store_registers): Turn into ...
	(linux_process_target::store_registers): ... this.
	* linux-low.h (class linux_process_target): Update.
	* lynx-low.cc (lynx_target_ops): Update.
	(lynx_fetch_registers): Turn into ...
	(lynx_process_target::fetch_registers): ... this.
	(lynx_store_registers): Turn into ...
	(lynx_process_target::store_registers): ... this.
	* lynx-low.h (class lynx_process_target): Update.
	* nto-low.cc (nto_target_ops): Update.
	(nto_fetch_registers): Turn into ...
	(nto_process_target::fetch_registers): ... this.
	(nto_store_registers): Turn into ...
	(nto_process_target::store_registers): ... this.
	* nto-low.h (class nto_process_target): Update.
	* win32-low.cc (win32_target_ops): Update.
	(win32_fetch_inferior_registers): Turn into ...
	(win32_process_target::fetch_registers): ... this.
	(win32_store_inferior_registers): Turn into ...
	(win32_process_target::store_registers): ... this.
	* win32-low.h (class win32_process_target): Update.