MIPS: Alchemy: physmap-flash for all devboards

Replace the devboard NOR MTD mapping driver with physmap-flash support.
Also honor the "swapboot" switch settings wrt. to the layout of the
NOR partitions.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Acked-By: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>