SPL: FIT: improve error handling

SPL: FIT: improve error handling

At the moment we ignore any errors due to missing FIT properties,
instead go ahead and calculate our addresses with the -1 return value.
Fix this and bail out if any of the mandatory properties are missing.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Tested-by: Kever Yang <kever.yang@rock-chips.com>
Tested-by: Jagan Teki <jagan@openedev.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>