[tee] Rename SMC Message to SMC Function

Per ARM SMCCC nomenclature, a SMC call targets a function of a secure
monitor provided service. As such, the SMC parameters that make up an
SMC call should be referred to as a function call rather than a message.
This will also help disambiguate from OP-TEE messages, which are an
optional parameters in shared memory.

This change is just a rename, no functionality changed.

Test: Compilation successful
Change-Id: Ieca80e27c777d07ed42997ba643201424ec0dbc2

[drivers][optee] Add barebones OP-TEE driver

OP-TEE is a Trusted OS designed for executing in the secure world of
Cortex-A cores using TrustZone. Interaction with OP-TEE is an RPC like
interface using the ARM Secure Monitor Call. The OP-TEE OS (BL32) is
initialized by ARM Trusted Firmware (BL31) prior to U-Boot (BL33).

This commit adds a not yet useful barebones driver that does nothing
more than check to see whether OP-TEE is available in the secure world.
For now, the platform driver will only attempt to initialize OP-TEE on
VIM2.

Test: Manually tested on VIM2 that the driver starts and binds when
OP-TEE is installed and that it doesn't when it is not installed.

Change-Id: I15315191d1a66f6841ec66e9bd7e7e8739aaa29e