ci: Enable experimental kernel stuff in armhf task

Base the task on --preset=dev-mode to ensure maximal coverage and add
the following:

   bitcoin-chainstate (experimental) ... ON
   libbitcoinkernel (experimental) ..... ON
   kernel-test (experimental) .......... ON

ci/test/00_setup_env_arm.sh

@@ -20,6 +20,7 @@ export CI_LIMIT_STACK_SIZE=1
 # -Wno-psabi is to disable ABI warnings: "note: parameter passing for argument of type ... changed in GCC 7.1"
 # This could be removed once the ABI change warning does not show up by default
 export BITCOIN_CONFIG=" \
+  --preset=dev-mode \
   -DREDUCE_EXPORTS=ON \
   -DCMAKE_CXX_FLAGS='-Wno-psabi -Wno-error=maybe-uninitialized' \
 "