mpc85xx: increase available RAM on Extreme Networks WS-AP3825i

mpc85xx: increase available RAM on Extreme Networks WS-AP3825i

The system-mamory size was page-aligned prior to this commit, only
enabling to use 192MB of system memory of the 256 available.

This was due to the system-memory being manually shrinked to reserve the
upper 1MB for the second-core bootpage in the loader as well as the OS.

Fix this properly in the loader and in Linux using reserved-memory
definitions. This enables the device to use 250MB of system memory.

Signed-off-by: David Bauer <mail@david-bauer.net>