qmx6_defconfig: update

- Update kernel
- Add u-boot configuration
- 6q_bootscript.txt is no more needed by new version of u-boot

Signed-off-by: Jérôme Pouiller <jezz@sysmic.org>
Tested-by: Gary Bisson <gary.bisson@boundarydevices.com>
[build test only]

Signed-off-by: Jérôme Pouiller <jezz@sysmic.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>