gallium: make pipe_context::begin_query return a boolean

GL_AMD_performance_monitor must return an error when a monitoring
session cannot be started.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Martin Peres <martin.peres@free.fr>
18 files changed