Provide a valid compatible string for the Ethernet switch node based on
the board including the switch. This allows us to have sane defaults and
silences the following warnings:

 arch/arm/boot/dts/bcm958522er.dt.yaml:
    ethernet-switch@36000: compatible: 'oneOf' conditional failed,
one
    must be fixed:
            ['brcm,bcm5301x-srab'] is too short
            'brcm,bcm5325' was expected
            'brcm,bcm53115' was expected
            'brcm,bcm53125' was expected
            'brcm,bcm53128' was expected
            'brcm,bcm5365' was expected
            'brcm,bcm5395' was expected
            'brcm,bcm5389' was expected
            'brcm,bcm5397' was expected
            'brcm,bcm5398' was expected
            'brcm,bcm11360-srab' was expected
            'brcm,bcm5301x-srab' is not one of ['brcm,bcm53010-srab',
    'brcm,bcm53011-srab', 'brcm,bcm53012-srab', 'brcm,bcm53018-srab',
    'brcm,bcm53019-srab']
            'brcm,bcm5301x-srab' is not one of ['brcm,bcm11404-srab',
    'brcm,bcm11407-srab', 'brcm,bcm11409-srab', 'brcm,bcm58310-srab',
    'brcm,bcm58311-srab', 'brcm,bcm58313-srab']
            'brcm,bcm5301x-srab' is not one of ['brcm,bcm58522-srab',
    'brcm,bcm58523-srab', 'brcm,bcm58525-srab', 'brcm,bcm58622-srab',
    'brcm,bcm58623-srab', 'brcm,bcm58625-srab', 'brcm,bcm88312-srab']
            'brcm,bcm5301x-srab' is not one of ['brcm,bcm3384-switch',
    'brcm,bcm6328-switch', 'brcm,bcm6368-switch']
            From schema:
    Documentation/devicetree/bindings/net/dsa/b53.yaml

Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>