ARM: dts: imx6sx: Fix LCDIF interrupt type

The LCDIF interrupt should be triggered by the rising edge of the
IRQ line because we only want the interrupt to trigger once per each
frame. It seems the LCDIF IRQ line cannot be explicitly de-asserted
by software, so the previous behavior before this patch, where the
interrupt was triggered by level-high status of the IRQ line, caused
the interrupt to fire again immediatelly after it was handled, which
caused the system to lock up due to the high rate of interrupts.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>