sparc64: fix sparse warnings in perf_event.c

Fix following sparse warnings:
kernel/perf_event.c:113:1: warning: symbol 'cpu_hw_events' was not declared. Should it be static?
kernel/perf_event.c:1156:6: warning: symbol 'perf_event_grab_pmc' was not declared. Should it be static?
kernel/perf_event.c:1172:6: warning: symbol 'perf_event_release_pmc' was not declared. Should it be static?
kernel/perf_event.c:1672:12: warning: symbol 'init_hw_perf_events' was not declared. Should it be static?
kernel/perf_event.c:1749:52: warning: incorrect type in argument 2 (different address spaces)
kernel/perf_event.c:1772:60: warning: incorrect type in argument 2 (different address spaces)
kernel/perf_event.c:1779:60: warning: incorrect type in argument 2 (different address spaces)

Define the functions static as they are not used outside this file.
Fix it so copy_from_user are supplied with pointers annotated _user

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