common/spl/spl_ram: Remove unused default

We ask for CONFIG_SPL_LOAD_FIT_ADDRESS in Kconfig, so we cannot define
it in C as a fall-back. However, this option previously was buried under
"if ... endif" Kconfig logic. Rework a number of config options to now
have more robust dependency lines so that we can ask this address when
needed. With that done, we can remove the fallback in spl_ram.c.

Signed-off-by: Tom Rini <trini@konsulko.com>