nitrogen6x: bootscript: clean up fbmem, add panel HDMI-1080P

The fbmem settings were wrong for fusion4, 1080P (LVDS) displays.

Add a setting for 1080P on HDMI:
	U-Boot > setenv panel HDMI-1080P
	U-Boot > saveenv && boot

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>