sparc32: fix sparse warnings in pcic.c

Fix following warnings:
pcic.c:164:14: warning: symbol 'pcic_regs' was not declared. Should it be static?
pcic.c:165:14: warning: symbol 'pcic_speculative' was not declared. Should it be static?
pcic.c:166:14: warning: symbol 'pcic_trapped' was not declared. Should it be static?
pcic.c:332:66: warning: Using plain integer as NULL pointer
pcic.c:344:66: warning: Using plain integer as NULL pointer
pcic.c:539:38: warning: Using plain integer as NULL pointer
pcic.c:677:1: warning: symbol 'pcic_pin_to_irq' was not declared. Should it be static?
pcic.c:783:6: warning: symbol 'pcic_nmi' was not declared. Should it be static?

Add extern for pcic_regs.
Define a few variables static.
Replace 0 with NULL.
Delete unused funtion pcic_pin_to_irq().
Include kernel.h so we could drop declaration of
t_nmi and add prototype for pcic_nmi.

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