x86/shim: don't permit HVM and PV_SHIM_EXCLUSIVE at the same time

x86/shim: don't permit HVM and PV_SHIM_EXCLUSIVE at the same time

This combination doesn't really make sense (and there likely are more);
in particular even if the code built with both options set, HVM guests
wouldn't work (and I think one wouldn't be able to create one in the
first place). The alternative here would be some presumably intrusive
#ifdef-ary to get this combination to actually build (but still not
work) again.

Fixes: 8b5b49ceb3d9 ("x86: don't include domctl and alike in shim-exclusive builds")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>