usb: phy: msm-hsphy: Support multiport PHY

Some targets have MSM HSPHY which support multiple ports.
These have additional port-specific registers such as HS_PHY_CTRL,
ALT_INTERRUPT_EN, and PARAMETER_OVERRIDE_X. Define offsets for
these as well as a new device tree parameter that specifies the
number of ports supported. Currently the max is 3.

Change-Id: I44c88f65fe2f305efaaa130f4f9dd624f27613c7
Signed-off-by: Tanya Finkel <tfinkel@codeaurora.org>