ARM: dts: NSP: Add a SRAB compatible string for each board

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 <[e-mail]>
Signed-off-by: Florian Fainelli <[e-mail]>

arch/arm/boot/dts/bcm958522er.dts

···
 &xhci {
 	status = "okay";
 };
+
+&srab {
+	compatible = "brcm,bcm58522-srab", "brcm,nsp-srab";
+};

arch/arm/boot/dts/bcm958525er.dts

···
 &xhci {
 	status = "okay";
 };
+
+&srab {
+	compatible = "brcm,bcm58525-srab", "brcm,nsp-srab";
+};

arch/arm/boot/dts/bcm958525xmc.dts

···
 &xhci {
 	status = "okay";
 };
+
+&srab {
+	compatible = "brcm,bcm58525-srab", "brcm,nsp-srab";
+};