intel-hid: Disable button array during suspend-to-idle

Notice that intel_button_array_enable() never disables the power
button which is the only one needed to wake up the system from
suspend-to-idle, so it can be safely called during suspend-to-idle
as well as during "regular" system suspend, and rearrange the
code in the driver's "suspend" and "resume" callbacks accordingly.

While at it, use pm_suspend_no_platform() to check if the current
suspend-resume cycle is suspend-to-idle, as that is the only
case when the device should be enabled while suspended.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>