USB: musb: partial DaVinci dm355 support

Partial support for DaVinci DM355, on the EVM board; peripheral
mode should work, once mainline merges DM355 support.  Missing:

  (a) renumbering the GPIO for DRVVBUS on the DM6446 EVM,
      when DAVINCI_N_GPIO increases;

  (b) disabling DM355_DEEPSLEEP.DRVVBUS_OVERRIDE so VBUS is
      driven according to the ID signal, if cpu_is_..._dm355()

The new PHY control bits are ignored on DM6446.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>