docs: Document some more hypercalls

docs: Document some more hypercalls

Some of these could probably do with some review from people who know
what these hypercalls actually do.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson.citrix.com>
---
 xen/include/public/arch-x86/xen.h |   30 ++++++++++++++++++++++++++++++
 xen/include/public/arch-x86_64.h  |   16 ++++++++++++++++
 xen/include/public/platform.h     |    4 ++++
 3 files changed, 50 insertions(+), 0 deletions(-)