clocksource/drivers/sp804: Add static for functions such as sp804_clockevents_init()

Add static for sp804_clocksource_and_sched_clock_init() and
sp804_clockevents_init(), they are only used in timer-sp804.c now.
Otherwise, the following warning will be reported:

drivers/clocksource/timer-sp804.c:68:12: warning: no previous prototype \
for 'sp804_clocksource_and_sched_clock_init' [-Wmissing-prototypes]
drivers/clocksource/timer-sp804.c:162:12: warning: no previous prototype \
for 'sp804_clockevents_init' [-Wmissing-prototypes]

Fixes: 975434f8 ("clocksource/drivers/sp804: Delete the leading "__" of some functions")
Fixes: 65f4d7dd ("clocksource/drivers/sp804: Remove unused sp804_timer_disable() and timer-sp804.h")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20201021012259.2067-2-thunder.leizhen@huawei.com