sparc32: fix sparse warnings in leon_kernel.c

Fix following warnings:
leon_kernel.c:40:15: warning: symbol 'leon3_gptimer_idx' was not declared. Should it be static?
leon_kernel.c:68:6: warning: symbol 'leon_eirq_setup' was not declared. Should it be static?
leon_kernel.c:273:13: warning: symbol 'leon_percpu_timer_ce_interrupt' was not declared. Should it be static?

Define symbols as static.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Daniel Hellstrom <daniel@gaisler.com>
Signed-off-by: David S. Miller <davem@davemloft.net>