devfreq: suppress platform driver bind / unbind feature.

For arm-memlat and bimc-hwmon platform driver does not
support the manual bind / unbind feature through sysfs,
when the governor is registered and started.

Suppress the bind / unbind calls using driver attribute.

Change-Id: I8287012e1e6931d80953382f3d625223315cec85
Signed-off-by: Santosh Mardi <gsantosh@codeaurora.org>