Fixes the 2.6.28-rc8-davinci1 booting on dm646x EVM.

davinci_psc_init is not being called for DM646x EVM, hence davinci_psc_mux
is not defined for DM646x. This is resulting in DM646x board not booting up.
Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>