am335x_evm: Correct DFU ALT settings for falcon mode

Now that we have falcon mode enabled, the partiton numbers for NAND have
changed, and we need to list entries for updating these parts of the
system.  While adding falcon mode entires for eMMC (raw), we round up
the limit on U-Boot for ease of math later.

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