Revert "block,elevator: use new hashtable implementation"

This reverts commit 2e5f61d4b6af537f69e9782c2782f0cae57e79c8.
Revert "hashtable: introduce a small and naive hashtable"

This reverts commit aec3361ad685257482a58ca45e022d43c197b86e.
Merge remote-tracking branch 'upstream/fk_4.2' into fk_4.2
Updated defconfig

Signed-off-by: kecinzer <kecinzer@gmail.com>