MAINTAINERS: fix stale TI DaVinci entries

Fix stale git tree entry. Patchwork project has
not been updated since TI DaVinci lost its
dedicated mailing list. Remove that entry.

Update mailing list to point to LAKML.

Acked-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>