LF-1081 arch: arm64: dts: imx8-cm4: correct INTMUX compatible string and

LF-1081 arch: arm64: dts: imx8-cm4: correct INTMUX compatible string and
interrupt specifier

Since upstream change:
commit 2fbb13961e74 ("irqchip: Add NXP INTMUX interrupt multiplexer support")

1. Compatible string change:
	nxp,imx-intmux -> fsl,imx-intmux

2. Two cells needed in interrupt specifier for INTMUX:
	the 1st cell: hw interrupt number
	the 2nd cell: channel index

Fixes: 9d18df5cc1bb (arm64: dts: imx8: cm40: move into a separate ss dtsi)
Fixes: bc431df69ac0 (arch: arm64: imx8qm: add lpi2c and intmux for CM41 subsystem)
Acked-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>