xsm: Consolidate xsm processing within domain control hypercall.

xsm: Consolidate xsm processing within domain control hypercall.

Consolidate all the 15 xsm calls from within do_domctl a single
routine that is only called in one place, xsm_domctl:

int xsm_domctl (struct xen_domctl *domctl);

The parameter to domctl is a pointer to the xen_domctl structure that
contains a union of all sub operational parameters.

The benefits of this patch include:

(1) Easier to maintain because there is one place in the entire
hypercall to check with the xsm, instead of 15 or more.

(2) New sub-operations don't also need to add a corresponding xsm
    function.

(3) Removes 178 lines of code.

(4) Enhanced security because of 1-4.

Signed-off-by: Mike D. Day <ncmike@us.ibm.com>