BACKPORT: tee: optee: add optee-specific shared pool implementation

This is simple pool that uses kernel page allocator. This pool can be
used in case OP-TEE supports dynamic shared memory.

Change-Id: Idd0b512ef577b38f61dabca60b86becf09a746cc
Signed-off-by: Volodymyr Babchuk <vlad.babchuk@gmail.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
(cherry picked from commit abd135ba215c05ca84f9809e6047db25fc28b835)
Signed-off-by: Victor Chong <victor.chong@linaro.org>