usb: ci13xxx_msm_hsic: Cleanup usage of vdd regulator

It is not required to distinguish beteween VDDCX or VDDCX corner voting.
Hence remove this usage and replace it with only vdd supply. Also add
required support for passing voltage levels or corner values using device
tree.

Change-Id: Ifef28729007a760dc724b65591cd39a6cdc6eb93
Signed-off-by: Mayank Rana <mrana@codeaurora.org>