optee: Add lib entries for sharing OPTEE code across ports

This patch adds code to lib to enable sharing of useful OPTEE code between
board-ports and architectures. The code on lib/optee/optee.c comes from the
TI omap2 port. Eventually the OMAP2 code will be patched to include the
shared code. The intention here is to add more useful OPTEE specific code
as more functionality gets added.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
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>
Tested-by: Peng Fan <peng.fan@nxp.com>