marvell: ap806_clock: add missing frequency modes

In the driver init routine the CPU clock frequency
value is obtained from a dedicated register. Until now
only part of the values were handled by the mv_ap806_clock
driver. Fix that by adding missing cases.

Submitted by: Zyta Szpak <zr@semihalf.com>
MFC after: 1 week
Obtained from: Semihalf
Sponsored by: Marvell