[partition] Introduce check for EFI partition type-and-size

Re-use the existing message about partition type and size,
since I don't want to introduce another message with all the
specifics; give a works-always message instead.

The check itself is also straightforward, avoiding all of the
nuances and technically-this-might-work cases: FAT32, 300MiB+.

FIXES #607

src/modules/partition/PartitionViewStep.cpp

@@ -445,7 +445,7 @@ PartitionViewStep::onLeave()
 
             QString message;
             QString description;
-            if ( !esp )
+            if ( !esp || ( esp && !PartUtils::isEfiFilesystemSuitable( esp ) ) )
             {
                 message = tr( "No EFI system partition configured" );
                 description = tr( "An EFI system partition is necessary to start %1."