usb: musb: dsps: use proper child nodes

This moves the two instances from the big node into two child nodes. The
glue layer ontop does almost nothing.

There is one devices containing the control module for USB (2) phy,
(2) usb and later the dma engine. The usb device is the "glue device"
which contains the musb device as a child. This is what we do ever since.

The new file musb_am335x is just here to prob the new bus and populate
child devices.

There are a lot of changes to the dsps file as a result of the changes:

- musb_core_offset
  This is gone. The device tree provides memory ressources information
  for the device there is no need to "fix" things

- instances
  This is gone as well. If we have two instances then we have have two
  child enabled nodes in the device tree. For instance the SoC in beagle
  bone has two USB instances but only one has been wired up so there is
  no need to load and init the second instance since it won't be used.

- dsps_glue is now per glue device
  In the past there was one of this structs but with an array of two and
  each instance accessed its variable depending on the platform device
  id.

- no unneeded copy of structs
  I do not know why struct dsps_musb_wrapper is copied but it is not
  necessary. The same goes for musb_hdrc_platform_data which allocated
  on demand and then again by platform_device_add_data(). One copy is
  enough.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>