winsys/radeon: Store GPU virtual memory addresses of BOs in a hash table

winsys/radeon: Store GPU virtual memory addresses of BOs in a hash table

This allows retrieving the existing BO and incrementing its reference count,
instead of creating a separate winsys representation for it, when the kernel
reports that the BO was already assigned a virtual memory address.

This fixes problems with XWayland using radeonsi and the
xf86-video-wlglamor driver, which calls GEM flink outside of the radeon
winsys code and creates BOs from the flinked names using the same DRM file
descriptor.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>