uboot-imx

mpc8641: Drop imaginary second flash bank, map 8MB

There's a lot of setup and foo for the second flash
bank.  The problem is, this board doesn't actually have one.
Clean this up.  Also, the flash is 8M in size.  Get rid
of the confusing aliased overmapping, and just map 8M.

Signed-off-by: Becky Bruce <becky.bruce@freescale.com>