package/optee-client: add option to configure TEE-based storage location

package/optee-client: add option to configure TEE-based storage location

OP-TEE provides the possibility of secure storage done by the
normal world OS via tee-supplicant.

The location is a compile-time value and by default it is /data/tee .
As this might not be suitable for all use-cases add an option to
set the CFG_TEE_FS_PARENT_PATH compile option.

Default value is still /data/tee as it was before adding this option.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>