net/bnxt: add Stingray support to core layer

net/bnxt: add Stingray support to core layer

- Moved P4 chip specific code under the P4 directory
- Added P45 skeleton code for SR to build on
- Add SR support in TRUFLOW core layer.
The TRUFLOW core or the tf-core is a shim layer which communicates with
the CFA block in the hardware.

Signed-off-by: Peter Spreadborough <peter.spreadborough@broadcom.com>
Signed-off-by: Jay Ding <jay.ding@broadcom.com>
Reviewed-by: Farah Smith <farah.smith@broadcom.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>