xen/grant-table: pre-populate kernel unmap ops for xen_gnttab_unmap_refs()

When unmapping grants, instead of converting the kernel map ops to
unmap ops on the fly, pre-populate the set of unmap ops.

This allows the grant unmap for the kernel mappings to be trivially
batched in the future.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

diff --cc arch/arm/include/asm/xen/page.h
Simple merge

diff --cc arch/arm/xen/p2m.c
Simple merge

diff --cc arch/x86/include/asm/xen/page.h
Simple merge

diff --cc arch/x86/xen/p2m.c
Simple merge

diff --cc drivers/xen/gntdev.c
Simple merge

diff --cc drivers/xen/grant-table.c
Simple merge

diff --cc include/xen/grant_table.h
Simple merge