imx6: geam6ul: Add default mtd nand partition table

geam6ul> mtdparts

device nand0 <nand>, # parts = 6
0: spl                 0x00200000      0x00000000      0
1: uboot               0x00200000      0x00200000      0
2: env                 0x00100000      0x00400000      0
3: kernel              0x00400000      0x00500000      0
4: dtb                 0x00100000      0x00900000      0
5: rootfs              0x1f600000      0x00a00000      0

Cc: Stefano Babic <sbabic@denx.de>
Cc: Matteo Lisi <matteo.lisi@engicam.com>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>