ext: Add missing header files symbols for Atmel SAM E70

Several missing symbols for same70q21 SoC are added:
- TC Channel Mode Register: Waveform Mode definitions
- Legacy peripheral IDs definitions
- DACC alternate pin functions

Jira: ZEP-976
Change-Id: Ia317cc864dd49f5ebfb2ce5914c4ea9f1dbea355
Signed-off-by: Piotr Mienkowski <piotr.mienkowski@gmail.com>