[RFC]VCHIQ: Convert vchiq from a platform driver to an on-demand library

[Electron752]

VCHIQ is very ulgy and getting the device tree documentation upstream is going to be a mess. I'm wondering if it would make sense to convert vchiq/vchi into a loadable library rather then a platform driver.

Here is what I'm thinking:

1. Make a separate #ifdef for the userland ioctl interface in the build configuration. It would default to no.
2. The vchiq core stays inactive until either the userland ioctl interface file is opened, or one of the internal drivers use it. At that point, the driver actually activates.
3. I don't think the firmware supports unloading vchiq but maybe it could in the future.

The only really tricky part would be to get the reference to the raspberrypi firmware driver. So maybe short term, the driver could stay a platform driver just stay dormant until it is actually used.