[host] dxgi: sleep until it's close to time to map

This change adds an average function to time how long it takes the GPU
to copy and map the texture, and then uses this average to sleep for 80%
of this average lowering CPU usage and potentially decreasing lock
contention.

common/CMakeLists.txt

@@ -28,6 +28,7 @@ set(COMMON_SOURCES
   src/framebuffer.c
   src/KVMFR.c
   src/countedbuffer.c
+  src/runningavg.c
 )
 
 add_library(lg_common STATIC ${COMMON_SOURCES})