colibri-imx6ull: imximage.cfg: integrate new 1GiB RAM variant

colibri-imx6ull: imximage.cfg: integrate new 1GiB RAM variant

Integrate new Toradex SKU 0062 Colibri iMX6ULL 1GB IT. This commit
basically adjusts three parameters of the RAM settings:

Increase density from 4Gb to 8Gb
Increase ROW address from 15 to 16
Increase tRFC (refresh command time) from 260 to 350

This timing is valid for all Toradex Colibri iMX6ULL SKUs

Related-to: ELB-4055, ELB-4057
Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>