Dedicated BOs waste memory and are also a significant cause of CPU
overhead when applications use hundreds of them per frame due to
all the work the kernel has to do to page in all these BOs for a job.
The UE4 Vehicle demo was hitting this causing it to freeze and stutter
under 1fps.

The hardware allows us to setup groups of 16 queries in consecutive
4-byte addresses, requiring only that each group of 16 queries is
aligned to a 1024 byte boundary. With this change, we allocate all
the queries in a pool in a single BO and we assign them different
offsets based on the above restriction. This eliminates the freezes
and stutters in the Vehicle sample.

One caveat of this solution is that we can only wait or test for
completion of a query by testing if the GPU is still using its BO,
which basically means that we can only wait for all active queries
in a pool to complete and not just the ones being requested by the
API. Since the Vulkan recommendation is to use a different query
pool per frame this should not be a big issue though.

If this ever becomes a problem (for example if an application does't
follow the recommendation and instead allocates a single pool and
splits its queries between frames), we could try to group queries
in a pool into a number of BOs to try and find a balance, but for
now this should work fine in most cases.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <mesa/mesa!10253>