ANDROID: GKI: power-supply: Add VOLTAGE_VPH power supply property

Add VOLTAGE_VPH power supply property to expose VPH voltage to user space.

Signed-off-by: Harry Yang <harryy@codeaurora.org>
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>
(cherry picked from commit bb818125c496cff3c299ee3a59be9b841e9c1e6f)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 150789066
Change-Id: I16eb6efe3eef5b173b0f1a66dc21ab6c4c5cb968