usb/isp1760: Let OF bindings depend on general CONFIG_OF instead of PPC_OF .

To be able to use the driver on other OF-aware architectures, too.
And add necessary OF related #includes to fix compilation error.

Signed-off-by: Joachim Foerster <joachim.foerster@missinglinkelectronics.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>