configs: tbs_a711: lower dram frequency

The dram chip on the tablet was changed. The new one requires a lower
frequency, so change it.

Frequency 564MHz was also stable in the tests, but use slightly lower one
to be on a safe side.

Signed-off-by: Tomas Novotny <tomas@novotny.cz>
[jagan: add MHz in commit message]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>