macchiatobin: bump kernel and u-boot versions

Bump Linux to 4.15 and U-Boot to 2018.01. Remove networking dts patches
since they has landed in Linux 4.15. Update readme.txt: fix mainline BSP
versions and update boot selection for board rev 1.3.

Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>