bootm: optee: Add a bootm command for type IH_OS_TEE

This patch makes it possible to verify the contents and location of an
OPTEE image in DRAM prior to handing off control to that image. If image
verification fails we won't try to boot any further.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Suggested-by: Andrew F. Davis <afd@ti.com>
Cc: Harinarayan Bhatta <harinarayan@ti.com>
Cc: Andrew F. Davis <afd@ti.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Kever Yang <kever.yang@rock-chips.com>
Cc: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Cc: Peng Fan <peng.fan@nxp.com>