xen/Kconfig: livepatch-build-tools requires debug information

xen/Kconfig: livepatch-build-tools requires debug information

The tools infrastructure used to build livepatches for Xen
(livepatch-build-tools) consumes some DWARF debug information present in
xen-syms to generate a livepatch (see livepatch-build script usage of readelf
-wi).

The current Kconfig defaults however will enable LIVEPATCH without DEBUG_INFO
on release builds, thus providing a default Kconfig selection that's not
suitable for livepatch-build-tools even when LIVEPATCH support is enabled,
because it's missing the DWARF debug section.

Fix by defaulting DEBUG_INFO to enabled when LIVEPATCH is.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>