Xen: ARM: Zero reserved fields of xatp before making hypervisor call

[ Upstream commit 0b47a6bd1150f4846b1d61925a4cc5a96593a541 ]

Ensure all reserved fields of xatp are zero before making
hypervisor call to XEN in xen_map_device_mmio().
xenmem_add_to_physmap_one() in XEN fails the mapping request if
extra.res reserved field in xatp is not zero for XENMAPSPACE_dev_mmio
request.

Signed-off-by: Jiandi An <anjiandi@codeaurora.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>