sysfs: add attribute specification for /sysfs/devices/.../coredump

This patch adds the specification for /sysfs/devices/.../coredump
which allows user-space to trigger a device coredump obtaining
binary data from the device for (fault) analysis. It relies on
CONFIG_DEV_COREDUMP being enabled.

Signed-off-by: Arend van Spriel <aspriel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>