Today, only a few platforms enable SPL_LOAD_FIT_FULL, and all enable
SPL_LOAD_FIT. As can be seen in usage, the FULL symbol is a superset of
the first symbol, not an alternative. Update Kconfig entries based on
this and simplify the only code which checks for either being set.
Signed-off-by: Tom Rini <trini@konsulko.com>