arm: dts: imx8mn-var-som: Fix broken EEPROM read

On branch WIP/17Oct2023, the EEPROM can no longer be read:

    U-Boot 2023.10-latest (Oct 17 2023 - 15:53:43 -0400)
    CPU:   Freescale i.MX8MNano Quad rev1.0 at 1200 MHz
    Reset cause: POR
    Model: Variscite VAR-SOM-MX8MN Symphony evaluation board
    var_read_som_eeprom: uclass_get_device_by_of_offset() failed: -19
    initcall failed at call 000000004022207c (err=-19)

Convert EEPROM-related properties to bootph-all so that the EEPROM can
also be read outside of SPL.

Fixes: 9e644284 ("dm: core: Report bootph-pre-ram/sram node as pre-reloc after relocation")
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>