MULTI DTB FIT

The purpose of this feature is to enable u-boot to select its DTB from a FIT
appended at the end of the binary.

Usually the DTB is selected by the SPL and passed down to U-Boot. But some
platforms don't use the SPL. In this case MULTI_DTB_FIT can used to provide
U-Boot with a choice of DTBs.
The relevant DTBs are packed into a FIT (list provided by CONFIG__OF_LIST). The
FIT is automatically generated at the end of the compilation and appended to
u-boot.bin so that U-Boot can locate it and select the correct DTB from inside
the FIT.
The selection is done using board_fit_config_name_match() (same as what the SPL
uses to select the DTB for U-Boot). The selection happens during fdtdec_setup()
which is called during before relocation by board_init_f().