usb: phy: qmp: Reset phy mode to USB on disconnect

USB qmp phy driver initializes phy mode to be combo (USB and DP) so
that both USB and DP (display port) can share the phy. This adds
additional refgen vote from qmp phy dp instance. Reset the phy mode
to USB only to avoid any additional refgen voting on physical
cable disconnect or DP 4 lane usecase. In case of DP 4 lane usecase,
DP driver will explicitly update the phy mode to DP only.

Change-Id: Ia6c4c11d8de8b111c2330d4ec7a0b3607d2b6f77
Signed-off-by: Vamsi Krishna Samavedam <vskrishn@codeaurora.org>