davinci: dm644x: Support for dm644x silicon revision 2.1

JTAG ID for DM644x silicon revision 2.1 has changed. An entry for the new
silicon revision needs to be added to the davinci_id structure. Without
this addition, EVMs with new silicon revision fail to boot the kernel.

Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>