MLK-17082-02 imx: add optee support for imx6sl

MLK-17082-02 imx: add optee support for imx6sl

  Add defconfig for tee support;
  Enable the TZASC support;
  Add env config for tee support.

Signed-off-by: Bai Ping <ping.bai@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
(cherry picked from commit 3535868b89df84d3e6554114f7867f9ef908ff01)
(cherry picked from commit 82a0b53092cdc0b025749f4d8f1cdfcc66e07db7)
(cherry picked from commit dc1602c2d7f9d1ff021e46a9187bbcb10f172a71)
(cherry picked from commit 181ae93e7b804db6dca4a0d2c3aaf547413428bb)
(cherry picked from commit 8d86ec747f3fed803ff523fc92ce64e0273db675)
(cherry picked from commit 389ac3ed2dc96cf50394f8f858f6e4ff941517f3)