dm646x: pass board revision info to kernel

add a function in board file to pass board revision
info to kernel. Revision number 0 and 1 are passed in
case of DM6467 and DM6467T respectively.

Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>