ARM: sheevaplug: change env location

This patch move the environment offset in sheevaplug.
The size of the u-boot binary is become too big.
Fix saving environments was result of corrupting the u-boot.

Signed-off-by: Gerald Kerma <drEagle@doukki.net>

 Changes in v2:
 - patch description

 Changes in v1:
 - fix sheevaplug environment offset
Signed-off-by: Prafulla Wadaskar <prafulla@marvell.com>