MIPS: sgi-ip22: Add prototypes for several functions to header

This fixes the following build warning:

arch/mips/sgi-ip22/ip22-time.c:119:18: error: no previous prototype for ‘indy_8254timer_irq’ [-Werror=missing-prototypes]
arch/mips/sgi-ip22/ip22-berr.c:89:6: error: no previous prototype for ‘ip22_be_interrupt’ [-Werror=missing-prototypes]
arch/mips/sgi-ip22/ip22-berr.c:113:13: error: no previous prototype for ‘ip22_be_init’ [-Werror=missing-prototypes]

Reported-by: k2ci <kernel-bot@kylinos.cn>
Signed-off-by: Genjian Zhang <zhanggenjian@kylinos.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>