configs: freescale_imx31_3stack: bump kernel version to 4.1.15_2.0.0_ga

configs: freescale_imx31_3stack: bump kernel version to 4.1.15_2.0.0_ga

Switch to the kernel of release 4.1.15_2.0.0_ga, as it builds properly with
gcc 5.x, which is now the default.

We add a linux config fragment to disable the framebuffer, to repair the
build for imx_v6_v7_defconfig.

Suggested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Signed-off-by: Julien Olivain <juju@cotds.org>
Tested-by: Julien Olivain <juju@cotds.org>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
[Thomas: adjust syntax in fragment.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>