sis190: add cmos ram access code for the SiS19x/968 chipset pair

More work is needed to handle correctly the PHY of the new devices
when connected to a 10Mb link but this change already helps some
users as is.

Fix for:
http://bugzilla.kernel.org/show_bug.cgi?id=9467

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: K.M. Liu <kmliu@sis.com.tw>
Cc: J. Gleacher <jgleacher@yahoo.com>
Cc: Alexandre Penasso Teixeira <alexandre@keepsoftware.com>
Cc: Arliton Rocha <arliton@gmail.com>
Cc: Juan Jose Pablos <juanjo@apertus.es>
Cc: Wipat Srutiprom <wipat.s@psu.ac.th>