xen/x86: Generate deep dependencies of features

xen/x86: Generate deep dependencies of features

Some features depend on other features.  Working out and maintaining the exact
dependency tree is complicated, so it is expressed in the automatic generation
script.

At runtime, Xen needs to be disable all features which are dependent on a
feature being disabled.  Because of the flattening performed at compile time,
runtime can use a single mask to disable all eventual features.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>