Add vcc50_hdmi regulator for Vyasa RK3288 board.

VCC50_HDMI is the real name used for this regulator as
per the schematics.

This regulator used for HDMI connector by detecting the
cable via HDMI_EN gpio and input rails are sourced from
VSUS_5V regulator.
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Link: https://lore.kernel.org/r/20200123134641.30720-3-jagan@amarulasolutions.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>