arm: K3: Introduce System Firmware loader framework

arm: K3: Introduce System Firmware loader framework

Introduce a framework that allows loading the System Firmware (SYSFW)
binary as well as the associated configuration data from an image tree
blob named "sysfw.itb" from an FS-based MMC boot media or from an MMC
RAW mode partition or sector.

To simplify the handling of and loading from the different boot media
we tap into the existing U-Boot SPL framework usually used for loading
U-Boot by building on an earlier commit that exposes some of that
functionality.

Note that this initial implementation only supports FS and RAW-based
eMMC/SD card boot.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>