We do the minimum which is to "pass" interrupts to HAL, which
makes the console smoother and will allow us to implement
interrupt based completion and console.
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

This adds a udbg and an hvc console backend for supporting a console
using the OPAL console interfaces.

On OPAL v1 we have hvc0 mapped to whatever console the system was
configured for (network or hvsi serial port) via the service
processor.

On OPAL v2 we have hvcN mapped to the Nth console provided by OPAL
which generally corresponds to:

	hvc0 : network console (raw protocol)
	hvc1 : serial port S1 (hvsi)
	hvc2 : serial port S2 (hvsi)

Note: At this point, early debug console only works with OPAL v1
and shouldn't be enabled in a normal kernel.
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Add definition of OPAL interfaces along with  the wrappers to call
into OPAL runtime and the early device-tree parsing hook to locate
the OPAL runtime firmware.
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>