qemu: block: Split up formatting of JSON props for 'raw' and 'luks' drivers

qemu: block: Split up formatting of JSON props for 'raw' and 'luks' drivers

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=1814975

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