* s390-nat.c (SUBOFF): Remove.
(s390_native_supply, s390_native_collect): New functions.
(supply_gregset, supply_fpregset): Use s390_native_supply.
(fill_gregset, fill_fpregset): Use s390_native_collect.
* s390-tdep.c (s390_pseudo_register_reggroup_p): Update comment.
(s390_unwind_pseudo_register): New function.
(s390_prologue_frame_unwind_cache): Unwind PSW address and mask
registers instead of PC and CC.
(s390_backchain_frame_unwind_cache): Likewise.
(s390_sigtramp_frame_unwind_cache): Do not unwind PC, CC, or
full GPR pseudos.
(s390_trad_frame_prev_register): New function.
(s390_frame_prev_register): Use it.
(s390_sigtramp_frame_prev_register): Likewise.
(s390_dwarf2_prev_register): Use s390_unwind_pseudo_register.
(s390_dwarf2_frame_init_reg): Unwind PSW address and mask. Use
special callback to unwind any pseudo.