board: ti: beagle_x15: enable 2GiB RAM

now that we have a revised board layout, we
can enable Second EMIF. This patch implements
it by have a unique 2GiB interleaved section.

Note that these are not optimized timings, but
I couldn't get it to crash on my board yet.

Signed-off-by: Felipe Balbi <balbi@ti.com>
board: ti: beagle_x15: improve EMIF configuration

Updated EMIF configuration that works

NYET-Signed-off-by: Franklin Cooper Jr. <fcooper@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>