board: samsung: add support for Samsung Exynos mobile device boards

board: samsung: add support for Samsung Exynos mobile device boards

Add support for a generic platform which intends to support multiple
boards powered by ARMv8 Samsung Exynos SoCs. Some important features
include:
 * Fastboot: This is present to provide an open alternative to Samsung's
   proprietary Odin protocol. The board file configures certain features
   for fastboot, such as a dynamically allocated fastboot buffer, and
   standardized (lowercase) partition aliases.
 * EFI: Kernel image can be loaded from an EFI partition. This
   adopts a standard booting process, which multiple OS distributions
   can rely on.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>