BACKPORT: tee: add register user memory

Added new ioctl to allow users register own buffers as a shared memory.

Change-Id: Icd25a3601884472fd42feac8aff03bb52e4d7e87
Signed-off-by: Volodymyr Babchuk <vlad.babchuk@gmail.com>
[jw: moved tee_shm_is_registered() declaration]
[jw: added space after __tee_shm_alloc() implementation]
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
(cherry picked from commit 033ddf12bcf5326b93bd604f50a7474a434a35f9)
Signed-off-by: Victor Chong <victor.chong@linaro.org>