dpdk: use v21.11 for DPDK

Build script checks out v21.11 release of DPDK.

Signed-off-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Malvika Gupta <malvika.gupta@arm.com>
Reviewed-by: Nathan Brown <Nathan.Brown@arm.com>

Change-Id: Ibddc5d5116a438d5c5061246b20da7e3cd2f0956