USB: otg/ulpi: improve ulpi phy detection.

Improve ulpi phy detection by utilizing the "scratch" register.
Allow unknown ulpi phy work without the need to hard-code the id.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>