new ofw_search_compatible()

[Ian Lepore]

While creating drivers that work for a variety of SoCs, I increasingly
find myself coding sequences such as:

	if (ofw_bus_is_compatible(dev, "fsl,imx51-fec"))
		sc->fectype = FECTYPE_IMX51;
	else if (ofw_bus_is_compatible(dev, "fsl,imx53-fec"))
		sc->fectype = FECTYPE_IMX53;
	else if (ofw_bus_is_compatible(dev, "fsl,imx6q-fec"))
		sc->fectype = FECTYPE_IMX6;
	else
		sc->fectype = FECTYPE_GENERIC;

That's a short list as an example, eventually that driver may support a
dozen SoCs.  I'd like to add a helper routine that turns this into a
table lookup, patch attached.  Any objections?  It turns sequences such
as the above into:

 static struct ofw_compat_data compat_data[] = {
	{"fsl,imx51-fec", FECTYPE_IMX51},
	{"fsl,imx53-fec", FECTYPE_IMX53},
	{"fsl,imx6q-fec", FECTYPE_IMX6},
	{NULL,		  FECTYPE_NONE},
 };
 /* ... */
 sc->fectype = ofw_bus_search_compatible(dev, compat_data)->ocd_data;

The search routine by design can't return NULL unless you pass it a NULL
table pointer.  That lets you provide whatever "not found" value in the
table-end sentry that works best for the way your code is structured.

-- Ian

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