gdbserver/linux-low: turn 'process_qsupported' into a method

gdbserver/linux-low: turn 'process_qsupported' into a method

gdbserver/ChangeLog:
2020-04-02  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	Remove the 'process_qsupported' linux target op and let a concrete
	linux target define the op by overriding the op declaration in
	process_stratum_target.

	* linux-low.h (struct linux_target_ops): Remove the op.
	(class linux_process_target) <process_qsupported>: Remove.
	* linux-low.cc (linux_process_target::process_qsupported): Remove.
	* linux-x86-low.cc (class x86_target) <process_qsupported>: Declare.
	(x86_linux_process_qsupported): Turn into...
	(x86_target::process_qsupported): ...this.
	(the_low_target): Remove the op field.
	* linux-aarch64-low.cc (the_low_target): Remove the op
	field.
	* linux-arm-low.cc (the_low_target): Ditto.
	* linux-bfin-low.cc (the_low_target): Ditto.
	* linux-crisv32-low.cc (the_low_target): Ditto.
	* linux-m32r-low.cc (the_low_target): Ditto.
	* linux-m68k-low.cc (the_low_target): Ditto.
	* linux-ppc-low.cc (the_low_target): Ditto.
	* linux-s390-low.cc (the_low_target): Ditto.
	* linux-sh-low.cc (the_low_target): Ditto.
	* linux-tic6x-low.cc (the_low_target): Ditto.
	* linux-tile-low.cc (the_low_target): Ditto.
	* linux-xtensa-low.cc (the_low_target): Ditto.