nxp defconfigs: bump kernel version to 4.1.15

nxp defconfigs: bump kernel version to 4.1.15

There is a 1.1.0_ga release, and a 1.1.1_patch release. The
patch release appears to be only for i.MX6UL, so it is bumped
to 1.1.1_patch, while the other are 1.1.0_ga.

Signed-off-by: Andrew Webster <awebster@arcx.com>
Reviewed-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>