ARM: OMAP2+: gpmc: Add device tree documentation for elm handle

In case ELM module available, omap2 NAND driver can opt for hardware
correction method for bit flip errors in NAND flash with BCH. Hence the
detection of ELM module is done through devicetree population of elm_id.
This patch update device tree documentation for gpmc-nand for elm-id
data population.
Signed-off-by: NPhilip Avinash <avinashphilip@ti.com>
Signed-off-by: NTony Lindgren <tony@atomide.com>

Documentation/devicetree/bindings/mtd/gpmc-nand.txt

@@ -29,6 +29,9 @@ Optional properties:
 		"bch4"		4-bit BCH ecc code
 		"bch8"		8-bit BCH ecc code
 
+ - elm_id:	Specifies elm device node. This is required to support BCH
+ 		error correction using ELM module.
+
 For inline partiton table parsing (optional):
 
  - #address-cells: should be set to 1
@@ -46,6 +49,7 @@ Example for an AM33xx board:
 		#address-cells = <2>;
 		#size-cells = <1>;
 		ranges = <0 0 0x08000000 0x2000>;	/* CS0: NAND */
+		elm_id = <&elm>;
 
 		nand@0,0 {
 			reg = <0 0 0>; /* CS0, offset 0 */