Update musb/davinci.c and Kconfig for the newish DM355 chips:

 - Support new controls:
    * PHY control bits for swapping D+/D- signals, OTG powerdown
    * DRVVBUS control bits
 - The DM355 EVM board swaps D+/D- for better signal integrity
 - Use clk_enable()/clk_disable() now that they work right

Plus some minor cleanup:  "void __iomem *" pointers work right now
(after some arch/arm changes), the DM6446 EVM stuff vanishes more
completely on other boards.

Eventually the board-specific stuff should move out of this part of
the driver, but that will affect more generic MUSB code.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>