Update m68k port for unwinder changes.

Update m68k port for unwinder changes.
* m68k-tdep.c (m68k_frame_cache): Expect this_frame.
(m68k_frame_this_id, m68k_frame_prev_register): Update signature.
(m68k_frame_unwind): Use default_frame_sniffer.
(m68k_frame_sniffer): Remove.
(m68k_frame_base_address): Expect this_frame.
(m68k_dummy_id): Renamed from m68k_unwind_dummy_id.  Expect
this_frame.
(m68k_gdbarch_init): Use set_gdbarch_dummy_id,
dwarf2_append_unwinders, and frame_unwind_append_unwinder.
* m68klinux-tdep.c (m68k_linux_pc_in_sigtramp): Expect frame_info
parameter instead of pc value.
(m68k_linux_get_sigtramp_info, m68k_linux_sigtramp_frame_cache):
Expect this_frame.
(m68k_linux_sigtramp_frame_this_id)
(m68k_linux_sigtramp_frame_prev_register)
(m68k_linux_sigtramp_frame_sniffer): Update signature.
(m68k_linux_sigtramp_frame_unwind): Use
m68k_linux_sigtramp_frame_sniffer.
(m68k_linux_init_abi): Use frame_unwind_append_unwinder.

* m68klinux-nat.c (store_register): Fix typo.