sparc64: fix sparse warning in kgdb_64.c

Fix following warnings:
kgdb_64.c:114:18: warning: symbol 'smp_kgdb_capture_client' was not declared. Should it be static?
kgdb_64.c:161:17: warning: symbol 'kgdb_trap' was not declared. Should it be static?

Add proper prototypes

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>