optee-{os,examples,client,test}: Build out of tree

Modifies the optee recipes to all build out of tree. This is cleaner and
helps prevent build error from stale builds when dependencies change.
Also allows the elimination of the OPTEEOUTPUTMACHINE variable in
optee-os.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Reviewed-by: Diego Sueiro <diego.sueiro@arm.com>
Reviewed-by: Denys Dmytriyenko <denys@ti.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>