qemuBlockStorageSourceGetFormatRawProps aggregated both formats but
since we now have props specific for either of those formats it's
unwanted to aggregate the code such way. Split out the 'luks' props
formatter into qemuBlockStorageSourceGetFormatLUKSProps.

The wrong separation demonstrates istself on formatting of the 'size'
and 'offset' attributes for the 'luks' driver which does not conform
to the qapi schema.

https://bugzilla.redhat.com/show_bug.cgi?id=1814975Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>