ARM: dts: dm816x: Correct NAND support nodes

The ELM node in dm816x.dtsi needs to declare the correct compatible
value here as per the binding only one value is correct, and the current
driver handles it correctly.  We then add pinmux information for the
NAND found on the EVM so that we do not rely on the ROM to do this for
us, and also so that we do not try and probe NAND before we probe the
ELM.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Roger Quadros <rogerq@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Mihail Grigorov <michael.grigorov@konsulko.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>