USB: phy-msm-qusb: Add support s/w enable of D+ pull-up in QUSB2 PHY

Adds support for s/w enable of VBUS presence on connect.
This allows for the D+ line to go high.

Also disables D+ pull-up on disconnect.

Change-Id: Ie5eb7774d13fd8bc36ac8c6ecf48894394d26229
Signed-off-by: Mayank Rana <mrana@codeaurora.org>