powerpc: defconfigs: add MTD_SPI_NOR (new dependency for M25P80)

These defconfigs contain the CONFIG_M25P80 symbol, which is now
dependent on the MTD_SPI_NOR symbol. Add CONFIG_MTD_SPI_NOR to satisfy
the new dependency.

At the same time, drop the now-nonexistent CONFIG_MTD_CHAR symbol.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Scott Wood <scottwood@freescale.com>