Check all compatible strings on uart devices in powerpc

[jhibbits]

Summary

Some device trees put "fsl,ns16650" first in the compatible list. This causes
the probe code to choke, even though the device is compatible with ns16650, and
has it listed later in the tree.

Test Plan

Boot the kernel

[andrew]

You might want to also look at how we find the correct uart in uart_bus_fdt.c. We have a linker set to enumerate all drivers we support. They then provide a struct ofw_compat_data with the compat string and uart class.

[jhibbits]

Add a new ofw_bus_ function. This reuses the existing name of an
internal(static) function, and renames the static function to _int (couldn't
think of a better name).

[jhibbits]

In D7676#159503, @andrew wrote:

You might want to also look at how we find the correct uart in uart_bus_fdt.c. We have a linker set to enumerate all drivers we support. They then provide a struct ofw_compat_data with the compat string and uart class.

Right, uart_cpu_powerpc.c's getdev() should be getting called by way of uart_bus_fdt.c.

[nwhitehorn]

Looks good. Thanks!