sparc: Make LDC use common iommu poll management functions

Note that this conversion is only being done to consolidate the
code and ensure that the common code provides the sufficient
abstraction. It is not expected to result in any noticeable
performance improvement, as there is typically one ldc_iommu
per vnet_port, and each one has 8k entries, with a typical
request for 1-4 pages.  Thus LDC uses npools == 1.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David S. Miller <davem@davemloft.net>