cgroup_misc: add kernel-doc comments for enum misc_res_type

Fully document enum misc_res_type with kernel-doc comments to prevent
kernel-doc warnings:

misc_cgroup.h:12: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Types of misc cgroup entries supported by the host.
misc_cgroup.h:12: warning: missing initial short description on line:
 * Types of misc cgroup entries supported by the host.

Fixes: a72232ea ("cgroup: Add misc cgroup controller")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: cgroups@vger.kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>