pseries: Consolidate RTAS loading

pseries: Consolidate RTAS loading

At each system reset, the pseries machine needs to load RTAS (the runtime
portion of the guest firmware) into the VM.  This means copying
the actual RTAS code into guest memory, and also updating the device
tree so that the guest OS and boot firmware can locate it.

For historical reasons the copy and update to the device tree were in
different parts of the code.  This cleanup brings them both together in
an spapr_load_rtas() function.

Signed-off-by: David Gibson <[email protected]>
Reviewed-by: Alexey Kardashevskiy <[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Reviewed-by: Michael Roth <[email protected]>