translate: move real_host_page setting to -common

Move the size and mask globals for the "real" host page size to
translate-common. This is to allow system-level code to use
REAL_HOST_PAGE_ALIGN and friends in builds which hide translate-all
behind arch-obj.

Cc: dgilbert@redhat.com
Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Message-Id: <b437638691f044bc690a7f03b1240c8b0f34ab57.1441614289.git.crosthwaite.peter@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>