Remove xml files from gdbserver

For ports which use new target descriptions, this patch removes
the xml files from being built into gdbserver,

Alan.

2018-03-21 Alan Hayward  <alan.hayward@arm.com>

gdbserver/
	* configure.srv (aarch64*-*-linux*): Don't include xml.
	(i[34567]86-*-cygwin*): Likewise.
	(i[34567]86-*-linux*): Likewise.
	(i[34567]86-*-lynxos*): Likewise.
	(i[34567]86-*-mingw32ce*): Likewise.
	(i[34567]86-*-mingw*): Likewise.
	(i[34567]86-*-nto*): Likewise.
	(tic6x-*-uclinux): Likewise.
	(x86_64-*-linux*): Likewise.
	(x86_64-*-mingw*): Likewise.
	(x86_64-*-cygwin*): Likewise.