UPSTREAM: usb: of: add an api to get dr_mode by the phy node

UPSTREAM: usb: of: add an api to get dr_mode by the phy node

Some USB phy drivers have different handling for the controller in each
dr_mode. But the phy driver does not have visibility to the dr_mode of
the controller.

This adds an api to return the dr_mode of the controller which
associates the given phy node.

Change-Id: I2bdf7ba8fbff03e8dd33a2f4642b4455bcdabd29
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
(cherry picked from commit 98bfb39466954c69d2a448e6ddcab6d91cd48e25)
Signed-off-by: Wu Liang feng <wulf@rock-chips.com>