IB/ehca: Tolerate dynamic memory operations before driver load

Implement toleration of dynamic memory operations and 16 GB gigantic
pages, where "toleration" means that the driver can cope with dynamic
memory operations that happen before the driver is loaded.  While the
ehca driver is loaded, dynamic memory operations are still prohibited
by returning NOTIFY_BAD from the memory notifier.

On module load the driver walks through available system memory,
checks for available memory ranges and then registers the kernel
internal memory region accordingly.  The translation of address ranges
is implemented via a 3-level busmap.

Signed-off-by: Hannes Hering <hering2@de.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>