mfd: do tcb6393xb state restore on resume only if requested

As requested by Ian make state restore only if it's requested
by platform data: some platforms do correctly save the state of
the chip during suspend/resume, but some (like tosa) incorrectly
power off the chip at suspend, so the driver supports restoring
some bits of the tc6393xb state (not full, merely enough to support
resume on tosa). With this patch this code is disabled by default.

Signed-off-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Acked-by: Ian Molton <spyro@f2s.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>