Add support for v5.18 tee shm pool changes

The tee shm pool has changed in commit d88e0493a054 of the Linux kernel
in a breaking way. Instead of having a pool manager with two pools now
only a single pool is being used.
This patch adds support for the simplified shm pool while maintaining
compatibility with earlier kernel versions too.

Signed-off-by: Imre Kis <imre.kis@arm.com>
Change-Id: I7bc8b5e5e1ca8c0552ec9e78023a62cd1ebd154c