Hey Siddharth,
Assuming you are using SDK7, all device tree files are under board-support/linux3.12XXX/arch/arm/boot/dts
I can't tell you which file to look in unless I know what board you are using or using as a reference. For my board the design is similar to the beaglebone, so the files to edit were am335x-bone-common.dtsi and am335x-bone.dts
Also, the naming convention of device tree starts mmc0 off as mmc1, and mmc1 as mmc2 etc etc..
