davinci: Handle pinmux conflict between mmc/sd and nor flash

On DA850/OMAP-L138 EVM, MMC/SD and NOR Flash share
some of the AEMIF pins. This patch prints out a warning
during booting, if both MMC/SD and NOR Flash are enabled
in kernel menuconfig.

If both MMC/SD and NOR Flash are enabled, only MMC/SD
will work correctly.

Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>