anv: Disable VF statistics for blorp and SOL memcpy

anv: Disable VF statistics for blorp and SOL memcpy

In order to get accurate statistics, we need to disable statistics for
blits, clears, and the surface state memcpy at the top of each secondary
command buffer.  There are two possible approaches to this:

 1) Disable before the blit/memcpy and re-enable afterwards

 2) Move emitting 3DSTATE_VF_STATISTICS from initialization and make it
    part of pipeline state and then just disabale statistics before
    blits and memcpy operations.

Emitting 3DSTATE_VF_STATISTICS should be fairly cheap so it doesn't
really matter which path we take.  We choose the second option as it's
more consistent with the way the rest of the statistics are enabled and
disabled.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>