Au1200: IDE driver build fix

The driver fails to compile with CONFIG_BLK_DEV_IDE_AU1XXX_MDMA2_DBDMA enabled:

drivers/ide/mips/au1xxx-ide.c: In function `auide_build_dmatable':
drivers/ide/mips/au1xxx-ide.c:256: error: implicit declaration of function
`sg_virt'
drivers/ide/mips/au1xxx-ide.c:275: error: implicit declaration of function
`sg_next'
drivers/ide/mips/au1xxx-ide.c:275: warning: assignment makes pointer from
integer without a cast

Fix this by including <linux/scatterlist.h>. While at it, remove the #include's
without which the driver happily builds.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>