package/e2fsprogs: add option for e2scrub

package/e2fsprogs: add option for e2scrub

The e2scrib tool has various requirements:

  - e2scrub and its associated helpers, are bash scripts

  - e2scrub_all depends on coreutils' readlink; busybox readlink is
    missing some options:
        readlink: invalid option -- 'e'

  - by design, e2scrub only works on an LVM volume

Add an option to enable e2scrub. This is probably seldom used, so it
does not warrant the usual dance about BR2_PACKAGE_BUSYBOX_SHOW_OTHERS
and selecting the tools; we can just depend on the required tools.

Signed-off-by: Tian Yuanhao <tianyuanhao@aliyun.com>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: James Hilliard <james.hilliard1@gmail.com>
[yann.morin.1998@free.fr:
  - add a kconfig option like for other tools
  - move the conditions to that new option
  - reword the commit log accordingly
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>