gallium: add the concept of batch queries

gallium: add the concept of batch queries

Some drivers (in particular radeon[si], but also freedreno judging from
a quick grep) may want to expose performance counters that cannot be
individually enabled or disabled.

Allow such drivers to mark driver-specific queries as requiring a new
type of batch query object that is used to start and stop a list of queries
simultaneously.

v3: adjust recently added nv50 queries

v2: documentation for create_batch_query

Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Tested-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>