S390: Add guarded-storage register support to gdbserver

S390: Add guarded-storage register support to gdbserver

Enable gdbserver to deal with the new guarded-storage register sets.

gdb/gdbserver/ChangeLog:

	* configure.srv (s390*-*-linux*): Add s390-gs-linux64.o and
	s390x-gs-linux64.o to srv_regobj.  Add s390-gs-linux64.xml,
	s390x-gs-linux64.xml, s390-gs.xml, and s390-gsbc.xml to
	srv_xmlfiles.  Add s390-gs-linux64-ipa.o and
	s390x-gs-linux64-ipa.o to ipa_obj.
	* linux-s390-low.c (HWCAP_S390_GS): New define.
	(s390_fill_gs, s390_store_gs, s390_fill_gsbc, s390_store_gsbc):
	New functions.
	(s390_regsets): Add regsets for NT_S390_GS_CB and NT_S390_GS_BC.
	(s390_arch_setup): Check for guarded-storage support and choose
	appropriate tdesc.
	(initialize_low_arch): Invoke init_registers_s390_gs_linux64 and
	init_registers_s390x_gs_linux64.
	* linux-s390-tdesc.h (enum s390_linux_tdesc) <S390_TDESC_GS>: New
	enum value.
	(init_registers_s390x_gs_linux64, tdesc_s390x_gs_linux64)
	(init_registers_s390_gs_linux64, tdesc_s390_gs_linux64): Declare.