usb: musb: patches for v3.7 merge window

Here we have a bunch of miscellaneous cleanups and fixes
to the musb driver. It fixes a bunch of mistakes errors
which nobody has triggered before, so I'm not Ccing stable
tree.

We are finally improving OMAP's VBUS/ID Mailbox usage so
that we can introduce our PHY drivers properly. Also, we're
adding support for multiple instances of the MUSB IP in
the same SoC, as seen on some platforms from TI which
have 2 MUSB instances.

Other than that, we have some small fixes like not kicking
DMA for a zero byte transfer, or properly handling NAK timeout
on MUSB's host side, and the enabling of DMA Mode1 for any
transfers which are aligned to wMaxPacketSize.

All patches have been pending on mailing list for a long time
and I don't expect any big surprises with this pull request.