c6x: use early_init_dt_scan

Convert c6x to use new early_init_dt_scan function.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Mark Salter <msalter@redhat.com>
Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
Cc: linux-c6x-dev@linux-c6x.org