ARM: dts: stm32: Fix touchscreen IRQ line assignment on DHCOM

While 7e5f3155 ("ARM: dts: stm32: Fix LED5 on STM32MP1 DHCOM PDK2")
fixed the LED0 assignment on the PDK2 board, the same commit did not
update the touchscreen IRQ line assignment, which is the same GPIO line,
shared between the LED0 output and touchscreen IRQ input. To make this
more convoluted, the same EXTI input (not the same GPIO line) is shared
between Button B which is Active-Low IRQ, and touchscreen IRQ which is
Edge-Falling IRQ, which cannot be used at the same time. In case the LCD
board with touchscreen is in use, which is the case here, LED0 must be
disabled, Button B must be polled, so the touchscreen interrupt works as
it should.

Update the touchscreen IRQ line assignment, disable LED0 and use polled
GPIO button driver for Button B, since the DT here describes baseboard
with LCD board.

Fixes: 7e5f3155 ("ARM: dts: stm32: Fix LED5 on STM32MP1 DHCOM PDK2")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Cc: linux-stm32@st-md-mailman.stormreply.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>