ARM: dts: OMAP2+: remove uses of obsolete gpmc,device-nand

Remove all remaining uses of gpmc,device-nand that have been added since
the property was removed by commit f40739faba8e ("ARM: dts: OMAP2+:
Simplify NAND support").

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>