apm821xx: dts: append SoC compatible to DTS

apm821xx: dts: append SoC compatible to DTS

This patch appends the "apm,bluestone" or "amcc,apollo3g"
machine compatible string to the current device tree source.

Please note that unlike other archs the PPC DT code does
not regard the machine's compatible string as a priority
list. This is explained in the kernel's usage-model.txt as follows:
"PowerPC uses a slightly different scheme where it calls the .probe()
hook from each machine_desc, and the first one returning TRUE is used.
However, this approach does not take into account the priority of the
compatible list, and probably should be avoided for new architecture
support."

For this reason, the "apm,bluestone" compatible string can't be
added to the WNDR4700. As otherwise the target specific pci
fix-up code will get ignored and this causes the ath9k WIFI
to not get initialized.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>