ARM: sheevaplug: correct nand partition layout

ARM: sheevaplug: correct nand partition layout

Commit 1e3d640316 (ARM: sheevaplug: redefine MTDPARTS) changed the partition
layout (without any description why), but didn't change the offset/size to
load the kernel from or the root=/dev/mtdblockX in the bootargs.

The 3MB forseen for a kernel is furthermore too little. A 4.4 build of
mvebu_v5_defconfig is 3.6MB:

-rw-r--r-- 1 peko peko 3.6M Jan 16 20:24 uImage.kirkwood-sheevaplug

When device tree support for sheevaplug was added to the kernel in commit
ee514b381e (ARM: Kirkwood: Add dts files for Sheevaplug and eSATA
Sheevaplug) a default flash partition layout (used if mtdparts= isn't passed
on the command line / CONFIG_MTD_CMDLINE_PARTS isn't enabled) with 1MB for
u-boot / environment, 4MB for the kernel and the rest for the rootfs, so use
that layout here and adjust the kernel loading to match.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Stefan Roese <sr@denx.de>