doc: deprecate Xen support
doc: deprecate Xen support

Following the calls on the mailing list:
	http://dpdk.org/ml/archives/dev/2017-June/068151.html
The Technical Board decided to drop Xen dom0 support from EAL:
	http://dpdk.org/ml/archives/dev/2017-June/068615.html

Signed-off-by: Thomas Monjalon <5f50a84c1fa3bcff146405017f36aec1a10a9e38@monjalon.net>
Signed-off-by: Jianfeng Tan <4339d9ba3a87a0d192e405945005ff86667f7b0c@intel.com>
Acked-by: John McNamara <af31595c36a4239b9676e9b3a777d3e2f15a6c4d@intel.com>
Acked-by: Jerin Jacob <5bca7d2a432bc0f5422b70b2701a4e4fa32edd00@caviumnetworks.com>
Acked-by: Shahaf Shuler <59427d49da6f2b944fbf4cb5ee70ef3ac25f744f@mellanox.com>

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