rauc: add patch to make it build with Linux < 3.0

This commit adds a patch to RAUC that makes the eMMC boot partition
support optional. This allows RAUC to build successfully on systems
using Linux < 3.0.

Fixes:

  http://autobuild.buildroot.net/results/7e1cbeb458cb6536a36eae0d24cefb36edb22f55/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>