net: stmmac: Initial support for TBS

Adds the initial hooks for TBS support. This needs a 32 byte descriptor
in order for it to work with current HW. Adds all the logic for Enhanced
Descriptors in main core but no HW related logic for now.

Changes from v2:
- Use bitfield for TBS status / support (Jakub)
- Remove unneeded cache alignment (Jakub)
- Fix checkpatch issues

Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>