Setup early console for error handling

An abort during the pci scan or usb scan should expectedly return back
to the forth prompt gracefully. Due to the lack of the terminal setup
it tries to return to forth prompt but causes repeated
exceptions. Moreover, code never returns to forth prompt.

The patch sets up early console for gracefull handling for such
errors/aborts.

Suggested-by:  Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Add private HCALL to inform updated RTAS base and entry

This patch adds a private HCALL to inform qemu the updated
rtas-base and rtas-entry address when OS invokes the call
"instantiate-rtas". This is required as qemu allocates the
error reporting structure in RTAS space upon a machine check
exception and hence needs to know the updated RTAS.

Enhancements to qemu to handle the private HCALL, prepare
error log and invoke machine check notification routine
are in a separate patch.

Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>