usb: phy-msm-usb: Clear is_ext_chg_dcp flag on disconnect

On platforms that use SMB/PMI for charger detection, usb doesn't
exit LPM on DCP connect and marks is_ext_chg_dcp flag. This flag
is not cleared on disconnect if ID is GND which can happen with
special cables that support charging in host mode. If is_ext_chg_dcp
is set then on next SDP connection, driver ignores SDP and
treats that as DCP.

Fix this by clearing is_ext_chg_dcp flag during disconnect and allow
enumeration logic for SDP charger.

CRs-Fixed:1099336
Change-Id: I6dd6c40a2c123c787bb411acb432d8c6c3a4348e
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>