[SERIAL] SIIG 8-port serial boards support

This patch adds support for SIIG 8-port boards. These boards have 4 ports in
separate bars and another 4 ports in the single bar. Because of this strange
port arrangement these cards need special setup function. Fortunately no other
SIIG cards have more than 4 port, so this setup function could be used for them
too.

Signed-off-by: Andrey Panin <pazke@donpac.ru>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>