usb: phy: Expose new PHY callback for performing PHY reset

Add a new PHY callback for performing PHY reset, which is required
by some targets during their initialization sequence.
As usb_phy_reset name was already in use by local msm PHY APIs,
change the previous usb_phy_reset to msm_usb_phy_reset.

Change-Id: Ieb5099d12e107c123d8889058aa564d0b091d6f9
Signed-off-by: Maya Erez <merez@codeaurora.org>