usb: phy: Dual role sysfs class definition

This CL adds a new class to monitor and change
dual role usb ports from userspace. The usb
phy drivers can register to the dual_role_usb
class and expose the capabilities of the ports.
The phy drivers can decide on whether a specific
attribute can be changed from userspace by
choosing to implement the appropriate callback.

Cherry-picked from
https://android-review.googlesource.com/#/c/167310/



Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Bug: 21615151
Change-Id: Id1c4aaa97e898264d7006381a7badd029b5d9789