Revert "cgroup: Disable cgroup "memory" by default"

Revert "cgroup: Disable cgroup "memory" by default"

The feature is used for saving memory which is consumed by memcg-related
structure (32bytes per 4K page), but now it is no longer merged on the
latest raspberry pi kernel. So instead of enabling memory cgroup by
adding command to cmdline.txt while preserving this feature, in order to
enable memory cgroup by default, this reverts commit '35bbb61da9e2
("cgroup: Disable cgroup "memory" by default")'

Change-Id: I1830129125fb44b36bfe64f97fddf329ea795c3c
Signed-off-by: Dongwoo Lee <dwoo08.lee@samsung.com>