The bootpage for the second core is placed by U-Boot in the upper 128k
of syste-memory.
This could either be a reserved-area or deducted from the total
system-memory. As only the latter is parsed by the bootwrapper, reduce
the available system memory for linux in order to preserve the bootpage
from being overwritten.
Signed-off-by: David Bauer <mail@david-bauer.net>