ARM: DRA722: Add support for DRA71x Silicon Rev 2.1

DRA71x processors are reduced pin and software compatible
derivative of DRA72 processors.

Silicon Rev 2.1 is a minor variant of DRA71x Rev 2.0 with
various fixes including the following:
 - NAND boot fixes
 - ROM update for secure boot crypto enhancement

Signed-off-by: Vishal Mahaveer <vishalm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>