ARMv8: add the secure monitor firmware framework

This framework is introduced for ARMv8 secure monitor mode firmware.
The main functions of the framework are, on EL3, verify the firmware,
load it to the secure memory and jump into it, and while it returned
to U-Boot, do some necessary setups at the 'target exception level'
that is determined by the respective secure firmware.

So far, the framework support only FIT format image, and need to define
the name of which config node should be used in 'configurations' and
the name of property for the raw secure firmware image in that config.
The FIT image should be stored in Byte accessing memory, such as NOR
Flash, or else it should be copied to main memory to use this framework.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>