xen-gntalloc: Userspace grant allocation driver

This allows a userspace application to allocate a shared page for
implementing inter-domain communication or device drivers. These
shared pages can be mapped using the gntdev device or by the kernel
in another domain.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --cc drivers/xen/Kconfig
Simple merge

diff --cc drivers/xen/Makefile
Simple merge

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

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