arm64: dts: freescale: add NXP FRDM-IMX91S board support

arm64: dts: freescale: add NXP FRDM-IMX91S board support

Add DeviceTree support for the NXP FRDM-IMX91S development board based
on the i.MX91 SoC. FRDM-IMX91S is a cost-optimized variant of FRDM-IMX91
and differs in memory, storage, Ethernet, and PMIC configuration:

- 512MB LPDDR4 (FRDM-IMX91 uses 1GB)
- 256MB FlexSPI-NAND (FRDM-IMX91 uses 8GB eMMC)
- Single GbE port (FRDM-IMX91 has dual GbE)
- PMIC PF9453 (FRDM-IMX91 uses PCA9451A)

This DT enables:
- ADC1
- UART1 and UART5
- I2C bus and children nodes
- USB and related nodes
- uSDHC1 and uSDHC2
- FlexSPI NAND flash
- Watchdog3
- Ethernet (eqos)
- FlexCAN
- MQS

Link: https://www.nxp.com/design/design-center/development-boards-and-designs/FRDM-IMX91S
(FRDM-IMX91S board page)
Link: https://www.nxp.com/design/design-center/development-boards-and-designs/FRDM-IMX91
(FRDM-IMX91 board page)

Co-developed-by: Lei Xu <lei.xu@nxp.com>
Signed-off-by: Lei Xu <lei.xu@nxp.com>
Co-developed-by: Xiaofeng Wei <xiaofeng.wei@nxp.com>
Signed-off-by: Xiaofeng Wei <xiaofeng.wei@nxp.com>
Signed-off-by: Yanan Yang <yanan.yang@nxp.com>
Tested-by: Daniel Baluta <daniel.baluta@nxp.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>