Pull up following revision(s) (requested by tsutsui in ticket #1659):

sys/arch/m68k/m68k/reenter_syscall.s: revision 1.5
sys/arch/m68k/m68k/reenter_syscall.s: revision 1.6
sys/arch/m68k/m68k/reenter_syscall.s: revision 1.7

Replace magic numbers with proper macros prepared in assym.h.

No binary changes.

Note this is a preparation for a possible fix of PR port-m68k/55990.

Consistently use motorola style.  No binary changes.
Seems missed in rev 1.3:
https://mail-index.netbsd.org/source-changes/2013/08/01/msg046378.html

Plug kernel stack leaks in reenter_syscall() for setcontext(2).
This fixes long standing kernel crashes (MMU fault, address error,
and silent freeze by a double bus fault etc. seen for ~10 years)
caused by kernel stack overflow, especially on x68k and sun3 running
Xorg based servers.  See PR/55990 for more details.

"This change seems perfectly reasonable" from thorpej@ and
jklos@ also reported this also solved freeze of his mac68k system
with 10 megabyes of memory.

Should be pulled up to netbsd-9 and netbsd-8.

(martin)