kbuild: Use wildcard for driver subdirectories

Change-Id: Id1685c0b28ec8e3ab972a671af6f2de6f321c645
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: http://review.coreboot.org/9805
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
4 files changed