Add missing helper function to locate an already existing resource

This functionality is currently not available outside of
kernel/resource.c

It is needed in order to find the memory resource corresponding
to removable memory so that it can be cleanly removed.

Change-Id: Iedc785d0df5023c16c60bf2881e5602d45f2b809
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>
(cherry picked from commit 00d3c81438b3e3f827ae720afb17a2e79a604e1e)