BACKPORT: optee: support asynchronous supplicant requests

Adds support for asynchronous supplicant requests, meaning that the
supplicant can process several requests in parallel or block in a
request for some time.

Change-Id: Ifa77c329d33f6884fc7a64b3594be2b33def492c
Acked-by: Etienne Carriere <etienne.carriere@linaro.org>
Tested-by: Etienne Carriere <etienne.carriere@linaro.org> (b2260 pager=y/n)
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
(cherry picked from commit 1647a5ac175490d7dac2e74532e85b6197fc74e9)
Signed-off-by: Victor Chong <victor.chong@linaro.org>