spl: fit: move fdt_record_loadable out of ARCH_FIXUP_FDT_MEMORY guard

The fdt_record_loadable()-function was wedged between other functions
that were guarded by ARCH_FIXUP_FDT_MEMORY.  This could lead to linker
errors on some configurations.

With this change, fdt_record_loadable() is moved out of the
ARCH_FIXUP_FDT_MEMORY guard (plus I tried to retain alphabetical
ordering for functions by placing it appropriately).

References: 9f45aeb9 ("spl: fit: implement fdt_record_loadable")
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reported-by: Michal Simek <michal.simek@xilinx.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>