MAINTAINERS: Add boards/phytec/phyboard_lyra to TI K3

We dropped the am62x from the phyboard_lyra_am62x name. Afterwards,
the files section for the TI K3 Platforms doesn't fit anymore.
Add the phyboard_lyra directly as all kits for this carrier-boards
use a K3 SOC.

Signed-off-by: Daniel Schultz <d.schultz@phytec.de>