This commit adds a new variable OPTEE_OS_SDK, define by the optee-os
package, which points to the OPTEE SDK installed in STAGING_DIR. This
will allow other pakage to find this SDK more easily.
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
[Thomas: improve commit log, rename variable to just OPTEE_OS_SDK]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>