dt-bindings: display: bridge: tc358775: make stby gpio optional

For a normal operation, the stby GPIO is not needed.

The reset pin is required because once the PPI (PHY protocol interface)
is started, it can only be stopped by asserting the reset pin.

Signed-off-by: Michael Walle <mwalle@kernel.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
[tony@atomide.com: dropped regulator related changes]
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240225062008.33191-2-tony@atomide.com