svga: add num-commands-per-draw HUD query

svga: add num-commands-per-draw HUD query

This query shows the ratio of total commands vs. drawing commands sent
to the vgpu device.  This gives some idea of how many state changes
are sent per draw call.  The closer the ratio is to 1.0, the better.

Reviewed-by: Charmaine Lee <charmainel@vmware.com>
Reviewed-by: Neha Bhende <bhenden@vmware.com>