spl: Set spl_image->fdt_addr pointer for full fitImage configuration

Set the spl_image->fdt_addr pointer both for simple fitImage configuration
as well as full fitImage configuration, to let spl_perform_fixups() access
the DT and perform modifications to it if necessary.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@konsulko.com>