xen/x86: make "earlyprintk=xen" work better for PVH Dom0

xen/x86: make "earlyprintk=xen" work better for PVH Dom0

The xen_hvm_early_write() path better wouldn't be taken in this case;
while port 0xE9 can be used, the hypercall path is quite a bit more
efficient. Put that first, as it may also work for DomU-s (see also
xen_raw_console_write()).

While there also bail from the function when the first
domU_write_console() failed - later ones aren't going to succeed.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/4fd89dcb-cfc5-c740-2e94-bb271e432d3e@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>