Make the Docker image privileged

Otherwise kconfig_compiler won't work (needs statx, but it can be
whitelisted in Docker only with a version of libseccomp not available in
Leap 15.1)

.drone.yml

@@ -4,6 +4,7 @@ name: default
 steps:
     - name: build
       image: einar/kde
+      privileged: true
       pull: if-not-exists
       commands:
         - mkdir build