powerpc/pseries: Add support for dynamic dma windows

If firmware allows us to map all of a partition's memory for DMA on a
particular bridge, create a 1:1 mapping of that memory. Add hooks for
dealing with hotplug events. Dynamic DMA windows can use larger than the
default page size, and we use the largest one possible.

Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Documentation/kernel-parameters.txt

@@ -626,6 +626,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	disable=	[IPV6]
 			See Documentation/networking/ipv6.txt.
 
+	disable_ddw     [PPC/PSERIES]
+			Disable Dynamic DMA Window support. Use this if
+			to workaround buggy firmware.
+
 	disable_ipv6=	[IPV6]
 			See Documentation/networking/ipv6.txt.