Currently early_xmon() calls directly into debugger() if xmon=early is passed.
This ties the invocation of early xmon to the location of parse_early_param(),
which might change.

Tested on P5 LPAR and F50.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>