drm/panel: sitronix-st7789v: avoid hardcoding invert mode

While the default panel uses invert mode, some panels
require non-invert mode instead.

Reviewed-by: Michael Riesch <michael.riesch@wolfvision.net>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230714013756.1546769-12-sre@kernel.org