Allow default value of npools used for iommu to be configured from cmdline

Allow default value of npools used for iommu to be configured from cmdline

    The default value of the number of pools used by the pooled IOMMU
    allocator  in lib/iommu-common.c is a constant today (set at 16).
    It is possible that, for some platforms and some devices, the combination
    of latency and frequency of  iommu alloc/free  requests may be such
    as to trigger fragmentation within a pool, leading to iommu alloc failure.

    Reducing the number of pools (and thus increasing the pool size) can
    minimize the risk of those failures.

    This patch provides a command line hook to set the default number of
    pools at boot time.

 Ported to UEK4

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: Allen Pais <allen.pais@oracle.com>