Amit,
You will want to refer to the specific datasheet for your selected KeyStone2 device, since different devices will have different boot options available.
In general, the KeyStone2 device will have one core selected as the master core and that core will execute from the internal BOOT ROM. That core will then execute what is needed to initialize one or more peripherals and either actively download or passively wait for initial download of code. For a Linux boot, this initial download will usually be U-Boot code, but it could be anything else if something else is being used.
There are Bootloader User Guides for ARM and for DSP available on the Product Folders for the various K2 devices.
Regards,
RandyP