This was too hard to split ... this adds a number of features
to the SCOM user interface:

 - Support for indirect SCOMs

 - read()/write() interface now handle errors and retries

 - New ioctl() "raw" interface for use by debuggers
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: NEddie James <eajames@linux.vnet.ibm.com>
Reviewed-by: NAlistair Popple <alistair@popple.id.au>