video: bcm2835: use bus_to_phys() on FB address

video: bcm2835: use bus_to_phys() on FB address

The FB address is generated by the firmware running on the GPU/VideoCore
and is a "bus" address. This address is the other side of an IOMMU from
the ARM upon which U-Boot is running. Use bus_to_phys() to convert this
to an ARM physical address. Without this, U-Boot seems to work just fine,
but once the Linux kernel boots on an RPi2, accessing the FB memory often
causes a hard system hang.

This is related to:
122426d46e31 ARM: bcm2835: use phys_to_bus() for mbox
5c0beb5c58c8 usb: dwc2: use phys_to_bus/bus_to_phys
79340db7f1f6 ARM: bcm2835: implement phys_to_bus/bus_to_phys

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>