Add separate configuration flag for hardware ALS support.

A new flag config_hardware_automatic_brightness_available indicates
that the device has hardware support for automatic screen brightness management,
while config_automatic_brightness_available now indicates that automatic
brightness mode is available in general.

If config_automatic_brightness_available is true but config_hardware_automatic_brightness_available is false,
then automatic brightness mode support in PowerManager support will be used.

Bug b/2015734 (Ambient light sensor support in power manager)

Change-Id: I6cd888252043dd63df3c25a1d14c21a04a91ad28
Signed-off-by: Mike Lockwood <lockwood@android.com>