regulator: fan53555: add support for Halo HL7503 buck converter

Halo HL7503 is a digitally programmable buck converter that
outputs a voltage from 600 to 1394 mV from an input voltage of
2.5 to 5.25 V. Since the register mappings are compatible with
FAN53555, add a new vendor ID to support it.

Change-Id: I1112fcf59d8ef1c0b1615cc311992dcfc1cc54e9
Signed-off-by: Tirupathi Reddy <tirupath@codeaurora.org>