bcache-tools: Adding package.

This is the bcache tools, required to setup the linux bcache
feature of the Linux kernel.

[Thomas: use only one hook to create the missing directories, as
suggested by Yann.]

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>