LF-204 arm: dts: imx7d-sdb-epdc: disable hdmi sii902x

LF-204 arm: dts: imx7d-sdb-epdc: disable hdmi sii902x

there's pin conflict between epdc and sii902x, seeing following boot message:
[    4.736169] imx7d-pinctrl 30330000.iomuxc: pin MX7D_PAD_EPDC_DATA13 already requested by 2-0039; cannot claim for 306f0000.epdc
[    4.748188] imx7d-pinctrl 30330000.iomuxc: pin-26 (306f0000.epdc) status -22
[    4.755346] imx7d-pinctrl 30330000.iomuxc: could not request pin 26 (MX7D_PAD_EPDC_DATA13) from group epdcgrp0  on device 30330000.iomuxc
[    4.767766] imx_epdc_v2_fb 306f0000.epdc: Error applying setting, reverse things back

disable hdmi(sii902x) to make epdc work

Signed-off-by: Robby Cai <robby.cai@nxp.com>
Reviewed-by: Sandor Yu <Sandor.yu@nxp.com>