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

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

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

	Remote the 'supports_tracepoints' linux target op and let the
	concrete linux target define it by overriding the op declared in
	process_stratum_target.

	* linux-low.h (struct linux_target_ops): Remove the op.
	(class linux_process_target) <supports_tracepoints>: Remove.
	* linux-low.cc (linux_process_target::supports_tracepoints): Remove.
	* linux-x86-low.cc (class x86_target) <supports_tracepoints>:
	Declare.
	(x86_supports_tracepoints): Turn into...
	(x86_target::supports_tracepoints): ...this.
	(the_low_target): Remove the op field.
	* linux-aarch64-low.cc (class aarch64_target)
	<supports_tracepoints>: Declare.
	(aarch64_supports_tracepoints): Turn into...
	(aarch64_target::supports_tracepoints): ...this.
	(the_low_target): Remove the op field.
	* linux-ppc-low.cc (class ppc_target) <supports_tracepoints>:
	Declare.
	(ppc_supports_tracepoints): Turn into...
	(ppc_target::supports_tracepoints): ...this.
	(the_low_target): Remove the op field.
	* linux-s390-low.cc (class s390_target) <supports_tracepoints>:
	Declare.
	(s390_supports_tracepoints): Turn into...
	(s390_target::supports_tracepoints): ...this.
	(the_low_target): Remove the op field.
	* linux-arm-low.cc (the_low_target): Remove the op field.
	* 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-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.