Realtek cr: Add autosuspend function.

The autosuspend function can be disabled by unchecking the Macro
CONFIG_REALTEK_AUTOPM in kernel config file, by default, this macro is
turned on.

Signed-off-by: edwin_rong <edwin_rong@realsil.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>