[XEN][POWERPC] Create a Domain Foreign Map space

[XEN][POWERPC] Create a Domain Foreign Map space
The following patch creates a Domain Foreign Map space that is uses to
map granted memory into the Linear Map of the domain.  The Linear Map
of Linux is the is the Kernel Virtual address space where VA = PA +
PAGE_OFFSET.
Also:
 - lots of grant_* interfaces work now
 - mm.[ch] cleanups
 - first pass at extracting Page Table operations from PAPR interfaces
 - get_page_type() fix logic bug
 - recognize a grant table mapping by placing its gmfn at the end of
   real memory.
 - grant table usually mapped like an IO page, so force WIMG bits I=0
 - mfn_to_gmfn and pfn2mfn get WAY to complex, need get a simpler model in.
 - communicate the Domain Foreign Map to domains using /xen/foreign-map
 - make sure all bit definitions are UL where possible
 - now that we actually assign Xen heap pages to domains they must be
   relinquished
Signed-off-by: Jimi Xenidis <jimix@watson.ibm.com>
Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>