Currently the pre-console buffer can accumulate early log messages
and flush them to the serial console as soon as it becomes available.

This patch just adds one more pre-console buffer flushing point and
does all the same for the other consoles too. This is particularly
useful for the vga/hdmi/lcd console, where we can see all the older
messages now (except for the log messages from SPL).

Naturally, we don't want to get an extra copy of the log messages
on the serial console again at the second flushing point, so the
serial console has to be explicitly filtered out.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Tom Rini <trini@ti.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>