am335x_evm: Update eMMC falcon mode locations

The previous location used for the "args" portion of falcon mode was too
small to allow for a device tree to be saved there, so move the location
slightly and increase the size.  In addition, our previous kernel
location was part of the area we set aside for U-Boot itself, so move it
up a bit higher.

Signed-off-by: Tom Rini <trini@ti.com>
Reviewed-by: Peter Korsgaard <jacmet@sunsite.dk>