am37xx: anvl: Fix muxing for GPMC_WAIT1

Fix muxing for GPMC_WAIT1 as noted by Braden

Signed-off-by: Tony Lindgren <tony@atomide.com>
am37xx: anvl: Fix some environment variables

Let's use ext4 instead of ext3 on MMC. Then we have ubifs
rootfs on partition 6, and kernel is at 0x260000.

Signed-off-by: Tony Lindgren <tony@atomide.com>