ARM: dts: da850-lcdk: add unit name for memory node

Add unit name for memory node to squash the W=1 warning:

arch/arm/boot/dts/da850-lcdk.dtb: Warning (unit_address_vs_reg): /memory: node has a reg or ranges property, but no unit name

While at it, drop the device_type property from memory
node since its provided by da850.dtsi already.

Reviewed-by: David Lechner <david@lechnology.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>