Add an API to add and delete windows in the mvmbus(4) controller. This
will be used by the PCIe controller to set up the memory regions for the
PCIe devices. Also export the PCIe IO and MEM address regions. These
will be used to setup the PCIe extents.

ok kettenis@

Implement a driver for Marvell's Mbus bridge. This is the component
that lets e.g. the CPU access a USB controller or the USB controller
access the system's RAM. The bridge needs to be configured for the
devices before we can access the controller or a controller our memory.

Since it otherwise acts like a simplebus, simply attach simplebus once
we are finished.

"looks good to me" kettenis@

Implement a driver for Marvell's Mbus bridge. This is the component
that lets e.g. the CPU access a USB controller or the USB controller
access the system's RAM. The bridge needs to be configured for the
devices before we can access the controller or a controller our memory.

Since it otherwise acts like a simplebus, simply attach simplebus once
we are finished.

"looks good to me" kettenis@