package/kmsxx: needs headers >= 3.8

package/kmsxx: needs headers >= 3.8

kms++ uses V4L2_MEMORY_DMABUF, which was only introduced in linux-3.8.

Fixes:
    http://autobuild.buildroot.org/results/8dc/8dcc74586d68195c72a58cb4944d05dd9f935fa1/
    http://autobuild.buildroot.org/results/224/22467a530a146302ef74b11f69cb5cdc54240876/
    http://autobuild.buildroot.org/results/0e5/0e576ec01bbbf68a05216f4459a8a0613c39c141/

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>