build: communicate correct page size to linker

build: communicate correct page size to linker

This change communicates the common and maximum page sizes to the
linker, which allows us to use the built-in constants that it provides
to deal with page alignments.

We only support 4K pages today so the fact these are fixed is not too
much of an issue, but we will need to revisit this if we ever support
other page sizes.

Change-Id: I3358c51e70df794025ddf25209ae0e2a96550b0e
Signed-off-by: Chris Kay <chris.kay@arm.com>