nitrogen8m: initial board addition

nitrogen8m: add ddr/ddr_memory_map.h
nitrogen8m: u-boot update changes
nitrogen8m: turn off cameras
nitrogen8m: cameras reset/pwrdn use ODE
This limits the high level current to the pullup resistor.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

nitrogen8m: make sure MIPI to LVDS chip is disabled at bootup
nitrogen8m: add env_dev/part definition for upgrade script convenience
nitrogen8m: add missing variables for upgrade/boot scripts
nitrogen8m: reset boot_scripts if upgradeu fails
nitrogen8m: restore netboot command
Only requires to set 'tftpserverip' and 'nfsroot' variables

Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>