buildroot

configs/minnowboard_max: bump kernel to 4.6.1

Also, rebase kernel config and adapt kernel command line in grub config file
to follow mmc numbering change.

[Peter: drop now unused linux-4.4.config]
Signed-off-by: Vincent Stehlé <vincent.stehle@intel.com>
Cc: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Cc: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>