mfd: sta2x11-mfd: Add defines for some sta2x11 sctl registers

These are required for the clock infrastructure code to properly configure
and control the sta2x11 PLLs.

Signed-off-by: Davide Ciminaghi <ciminaghi@gnudd.com>
Acked-by: Alessandro Rubini <rubini@gnudd.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>