optee: Add support for arm,ffa-lend-pool

Hook OP-TEE dynamically allocated protected memory pools to the
"arm,ffa-lend-pool" driver. While the SMC transport platform device
resolves the pool through its DT "memory-region" property, the FF-A
transport lacks a device tree node and binds via ffa_lend_pool_attach().

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>