nios2: add nios2-generic board

nios2: add nios2-generic board

This is a generic approach to port u-boot for nios2 boards.
You may find the usage of this approach on the nioswiki,
http://nioswiki.com/DasUBoot

A fpga parameter file, which contains base address information
and drivers declaration, is generated from Altera's hardware system
description sopc file using tools.

The example fpga parameter file is compatible with EP1C20, EP1S10
and EP1S40 boards. So these boards can be removed after this commit.
Though epcs controller is removed to cut the dependency of altera_spi
driver.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Signed-off-by: Scott McNutt <smcnutt@psyent.com>