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 <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Tested-by: Heiko Stuebner <[email protected]>
Reviewed-by: Kever Yang <[email protected]>
Tested-by: Kever Yang <[email protected]>
Tested-by: Jagan Teki <[email protected]>
Reviewed-by: Jagan Teki <[email protected]>