sparc32: fix sparse warnings in process_32.h

Fix following warnings:
process_32.c:67:6: warning: symbol 'arch_cpu_idle' was not declared. Should it be static?
process_32.c:257:16: warning: symbol 'sparc_do_fork' was not declared. Should it be static?
process_32.c:411:5: warning: symbol 'dump_fpu' was not declared. Should it be static?

Add missing includes and add one missing prototype.

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