of: reserved-memory: Bypass rmem initialization check for carveouts

Pure carveouts (i.e. memory that is completely unmanaged by the
kernel) do not have any initialization routines associated
with them. So, ignore them when checking if a region has already
been initialized by the reserved memory framework.

Change-Id: Ied0db066a372751f40327460e583a81ad5b5429f
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>