buildroot

configs: chromebook snow: bump to linux 4.6.3

No significant changes but 4.6.3 moved parts of the device tree
into a different file, so dts patch must be updated.

[Peter: explicitly configure kernel headers for 4.6]
Signed-off-by: Alex Suykov <alex.suykov@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>