virDomainTimerCatchupDef: Change members to 'unsigned long long'

virDomainTimerCatchupDef: Change members to 'unsigned long long'

The struct used 'unsigned long' variables which we try to avoid due to
being different size on different architectures.

Convert the struct and use virXMLPropULongLong instead of virXPathULong
when parsing the XML.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>