ARM: dts: Fix USB dts configuration for dm816x

Commit 7800064b

 ("ARM: dts: Add basic dm816x device tree
configuration") added basic devices for dm816x, but I was not able
to test the USB completely because of an unconfigured USB phy, and
I only tested it to make sure the Mentor chips are detected and
clocked without a phy.

After testing the USB with actual devices I noticed a few issues
that should be fixed to avoid confusion:

- The USB id pin on dm8168-evm is hardwired and can be changed
  only by software. As there are two USB-A type connectors, let's
  start both in host mode instead of otg.

- The Mentor core is configured in such a way on dm8168-evm that
  it's not capable of multipoint at least on revision c board
  that I have.

- We need ranges for the syscon to properly set up the phy as
  children of the SCM syscon area.

- Let's not disable the second interface, the board specific
  dts files can do that if really needed. Most boards should
  just keep it enabled to ensure the device is idled properly.

Note that also a phy and several musb fixes are still needed to
make the USB to work properly in addition to this fix.

Cc: Brian Hutchinson <b.hutchman@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>