ARM: 8904/1: skip nomap memblocks while finding the lowmem/highmem boundary

adjust_lowmem_bounds() checks every memblocks in order to find the boundary
between lowmem and highmem. However some memblocks could be marked as NOMAP
so they are not used by kernel, which should be skipped while calculating
the boundary.

Signed-off-by: Chester Lin <clin@suse.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>