netdev: i82596 Ethernet needs <asm/cacheflush.h> on m68k

drivers/net/82596.c: In function 'init_rx_bufs':
drivers/net/82596.c:552: error: implicit declaration of function 'cache_clear'
drivers/net/82596.c: In function 'i596_start_xmit':
drivers/net/82596.c:1104: error: implicit declaration of function 'cache_push'

The driver still compiles on ia32 (CONFIG_APRICOT=y)
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>