arm64: dts: imx8mm-beacon: Fix ecspi2 pinmux

arm64: dts: imx8mm-beacon: Fix ecspi2 pinmux

[ Upstream commit a3e9f4d39dee371e8adde86443c1b62afb680260 ]

Early hardware did not support hardware handshaking on the UART, but
final production hardware did.  When the hardware was updated the chip
select was changed to facilitate hardware handshaking on UART3.  Fix the
ecspi2 pin mux to eliminate a pin conflict with UART3 and allow the
EEPROM to operate again.

Fixes: 0828ce17822e ("arm64: dts: imx8mm-beacon: Enable RTS-CTS on UART3")
Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>