local.conf: add support for Colibri iMX7
local.conf: add support for Colibri iMX7

Clean up the imx6 device tree setting, move to its kernel bbappend file.
Add imx7 build machine and EULA

Signed-off-by: Jason Liu <76a57ac72627ac6bc35b47c28a9937340c51b1c2@gumstix.com>

gumstix/meta-gumstix-extras,gumstix/meta-gumstix-extras,gumstix/meta-gumstix-extras