Add a second mapcache for grant mappings. The mapcache for grants needs to work with XC_PAGE_SIZE granularity since we can't map larger ranges than what has been granted to us. Like with foreign mappings (xen_memory), machines using grants are expected to initialize the xen_grants MR and map it into their address-map accordingly. CC: Manos Pitsidianakis <manos.pitsidianakis@linaro.org> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com> Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>