BACKPORT: tee: flexible shared memory pool creation

Makes creation of shm pools more flexible by adding new more primitive
functions to allocate a shm pool. This makes it easier to add driver
specific shm pool management.

Change-Id: I9ab51718083e0b86a47b9c56f32c57d69b43e30d
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Volodymyr Babchuk <vlad.babchuk@gmail.com>
(cherry picked from commit e2aca5d8928acb9cc9a87802b02102d4f9b9b596)
Signed-off-by: Victor Chong <victor.chong@linaro.org>