L4T R28.1 notes

As of 30 Jul 2017, the pyro-l4t-r28.1 branch supports Jetson TX1 and Jetson TX2 builds using L4T R28.1.

Only minimal testing has been performed so far, but core-image-sato images build, and most functionality tested appears to work OK.

Note that with R28.1, the Jetson TX1 boot sequence has been changed to include cboot in the chain of bootloaders, similar to the Jetson TX2. cboot loads U-Boot from the LNX partition in the eMMC.