modpost: Put .zdebug* section on white list

"as --compress-debug-sections" will generate compressed debug sections
with section names ".zdebug*".  This patch puts .zdebug* section on
white list.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>