epow: Add a device-node to represent EPOW functionality
epow: Add a device-node to represent EPOW functionality

Which includes a list of the supported EPOW classes

Signed-off-by: Benjamin Herrenschmidt <a7089bb6e7e92505d88aaff006cbdd60cc9120b6@kernel.crashing.org>

neelegup/skiboot,legoater/skiboot,cyrilbur-ibm/skiboot,cyrilbur-ibm/skiboot,legoater/skiboot,shenki/skiboot,jk-ozlabs/skiboot,stewart-ibm/skiboot,ddstreet/skiboot,mikey/skiboot,qemu/skiboot,legoater/skiboot,ddstreet/skiboot,apopple/skiboot,qemu/skiboot,stewart-ibm/skiboot,jk-ozlabs/skiboot,open-power/skiboot,apopple/skiboot,jk-ozlabs/skiboot,apopple/skiboot,ddstreet/skiboot,stewart-ibm/skiboot,qemu/skiboot,legoater/skiboot,qemu/skiboot,qemu/skiboot,open-power/skiboot,shenki/skiboot,neelegup/skiboot,open-power/skiboot,mikey/skiboot,mikey/skiboot,csmart/skiboot,open-power/skiboot,shenki/skiboot,open-power/skiboot,csmart/skiboot,csmart/skiboot,shenki/skiboot,shenki/skiboot,legoater/skiboot,neelegup/skiboot,cyrilbur-ibm/skiboot