docs: move vtpm from misc to man

vtpm.txt is referenced in xl.cfg man page. Convert it to pod,
move it to the man folder and update the reference. The man page
is named xen-vtmp to avoid any potential conflict with other
VTPM documentation.

Signed-off-by: Cédric Bosdonnat <cbosdonnat@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>

docs/INDEX

@@ -18,7 +18,6 @@ misc/xenstore-paths		Xenstore path documentation
 misc/distro_mapping		Distro Directory Layouts
 misc/dump-core-format		Xen Core Dump Format
 misc/vtd			VT-d HOWTO
-misc/vtpm			Virtual TPM
 misc/xen-error-handling		Xen Error Handling
 misc/xenpaging			Xen Paging
 misc/xsm-flask			XSM/FLASK Configuration