optee: allow to work without static shared memory

On virtualized systems it is possible that OP-TEE will provide
only dynamic shared memory support. So it is fine to boot
without static SHM enabled if dymanic one is supported.

Signed-off-by: Volodymyr Babchuk <vlad.babchuk@gmail.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>