ne: MIPS: Use platform_driver for ne on RBTX49XX

This patch lets RBTX49XX boards use generic platform_driver interface
for the ne driver.

* Use platform_device to pass ioaddr and irq to the ne driver.
* Remove unnecessary ifdefs for RBTX49XX from the ne driver.
* Make the ne driver selectable on these boards regardless of CONFIG_ISA

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Jeff Garzik <jeff@garzik.org>