xsm: Fix xsm_mmu_* and xsm_update_va_mapping hooks

xsm: Fix xsm_mmu_* and xsm_update_va_mapping hooks

This is an attempt to properly fix the hypervisor crash previously
described in
http://marc.info/?l=xen-devel&m=128396289707362&w=2

In looking into this issue, I think the proper fix is to move the
xsm_mmu_* and xsm_update_va_mapping hook calls later in the callers,
after more validation has been performed and the page_info struct is
readily available, and pass the page_info to the hooks. This patch
moves the xsm_mmu_normal_update, xsm_mmu_machphys_update and
xsm_update_va_mapping hook calls accordingly, and updates their
interfaces and hook function implementations.  This appears to resolve
the crashes for me.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>