[yocto] Yocto reference manual missing entries for MACHINE_DEVICETREE and KERNEL_DEVICETREE

[Elvis Dowson]

Hi Scott,
                I noticed that the yocto reference manual is missing entries for MACHINE_DEVICETREE and KERNEL_DEVICETREE variables.

I was trying to find out what the difference between the two were, and discovered that it's not described in the reference manual here:

http://www.yoctoproject.org/docs/1.5/ref-manual/ref-manual.html

Best regards,

Elvis Dowson