gallium: Add a f32 field to pipe_query_result

This will be used for the GL_FLOAT counter type of
AMD_performance_monitor.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
mesa/st: enable GL_AMD_performance_monitor

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
/bin/bash: q: command not found

This is based on the original patch of Christoph Bumiller.
(source: http://people.freedesktop.org/~chrisbmr/perfmon.diff)

V2: (Samuel Pitoiset)
 - Fix compilation
 - Improve the original code

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>