ppc4xx: Canyonlands: Change EBC bus config to drive always (no high-z)

ppc4xx: Canyonlands: Change EBC bus config to drive always (no high-z)

This patch fixes a problem only seen very occasionally on Canyonlands.
The NOR flash interface (CFI driver) doesn't work reliably in all cases.
Erasing and/or programming sometimes doesn't work. Sometimes with
an error message, like "flash not erased" when trying to program an
area that should have just been erased. And sometimes without any error
messages. As mentioned above, this problem was only seen rarely and with
some PLL configuration (CPU speed, EBC speed).

Now I spotted this problem a few times, when running my Canyonlands with
the following setup (chip_config):

1000-nor         - NOR  CPU:1000 PLB: 200 OPB: 100 EBC: 100

Changing the EBC configuration to not release the bus into high
impedance state inbetween the transfers (ATC, DTC and CTC bits set to 1
in EBC0_CFG) seems to fix this problem. I haven't seen any failure
anymore with this patch applied.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: David Mitchell <dmitchell@amcc.com>
Cc: Jeff Mann <MannJ@embeddedplanet.com>