ARM: dts: meson: switch TFLASH_VDD_EN pin to open drain on Odroid-C4

For the proper reboot Odroid-C4 board requires to switch TFLASH_VDD_EN
pin to the high impedance mode, otherwise the board is stuck in the
middle of loading early stages of the bootloader from SD card.

This can be achieved by using the OPEN_DRAIN flag instead if the
ACTIVE_HIGH, what will leave the pin in input to achieve high state (pin
has the pull-up) and solve the issue.

Suggested-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>