powerpc/p3060: remove all references to RCW bits EC1_EXT, EC2_EXT, and EC3

The EC1_EXT, EC2_EXT, and EC3 bits in the RCW don't officially exist on the
P3060 and should always be set to zero.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>