The Linux 4.0 kernel doesn't build with gcc 6.x, which is used since
the toolchain update in commit
193dfffa83 ("support/testing: use more
recent toolchains"). So let's update to Linux 4.11 instead (like the
existing Qemu x86 defconfig does), and update the kernel configuration
file accordingly.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>