board: Add support for Engicam i.CoreM6 DualLite/Solo boards

board: Add support for Engicam i.CoreM6 DualLite/Solo boards

Add initial support for Engicam i.CoreM6 DualLite/Solo board
with below features:
- U-Boot 2017.07-rc1
- Linux 4.11.5
- Default packages from buildroot

U-Boot 2017.07-rc1 has common u-boot defconfig for All i.CoreM6
variant boards, so this patch update the same along with
buildroot defconfig that reflect the common name.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>