powerps/pseries/dma: Add support for 2M IOMMU page size

The upcoming PAPR spec adds a 2M page size, bit 23 right after 16G page
size in the "ibm,query-pe-dma-window" call.

This adds support for the new page size. Since the new page size is out
of sorted order, this changes the loop to not assume that shift[] is
sorted.

This has now been tested and is known to work on a pre-release version
of phyp.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Leonardo Bras <leobras.c@gmail.com>
Reviewed-by: Frederic Barrat <fbarrat@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211006044735.1114669-1-aik@ozlabs.ru