regulator: fan53555: add support to disable suspend voltage configuration

Currently, fan53555 regulator driver always registers for
set_suspend_voltage. This force configures the regulator to
set suspend voltage switching to a different voltage selector.
However, this might not be preferred for certain applications.

Add a device tree parameter "fcs,disable-suspend" for the
regulator which when specified will disable suspend voltage
configuration.

CRs-Fixed: 968575
Change-Id: Ib9f450126482e606f3e057857b7a58800583519a
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>