Add framebuffer access wrapper infrastructure.

Create fbPrepareAccess macros to call into the driver to set up the
wfbReadMemory and wfbWriteWemory pointers.  Call these from fbGetDrawable and
fbGetStipDrawable.

Add the READ and WRITE macros, which expand to simple memory accesses for fb,
and calls through the function pointers for wfb.

Add fbFinishAccess macro to give the driver an opportunity to clean up.  Add
calls to this in the appropriate places.

fb/fbcompose.c

@@ -2652,6 +2652,7 @@ static void fbFetchSolid(PicturePtr pict, int x, int y, int width, CARD32 *buffe
     end = buffer + width;
     while (buffer < end)
         *buffer++ = color;
+    fbFinishAccess (pict->pDrawable);
 }
 
 static void fbFetch(PicturePtr pict, int x, int y, int width, CARD32 *buffer)
@@ -2670,6 +2671,7 @@ static void fbFetch(PicturePtr pict, int x, int y, int width, CARD32 *buffer)
     bits += y*stride;
 
     fetch(bits, x, width, buffer, indexed);
+    fbFinishAccess (pict->pDrawable);
 }
 
 #define MOD(a,b) ((a) < 0 ? ((b) - ((-(a) - 1) % (b))) - 1 : (a) % (b))
@@ -2921,8 +2923,10 @@ static void fbFetchTransformed(PicturePtr pict, int x, int y, int width, CARD32
 
     /* when using convolution filters one might get here without a transform */
     if (pict->transform) {
-        if (!PictureTransformPoint3d (pict->transform, &v))
+        if (!PictureTransformPoint3d (pict->transform, &v)) {
+            fbFinishAccess (pict->pDrawable);
             return;
+        }
         unit.vector[0] = pict->transform->matrix[0][0];
         unit.vector[1] = pict->transform->matrix[1][0];
         unit.vector[2] = pict->transform->matrix[2][0];
@@ -3352,6 +3356,8 @@ static void fbFetchTransformed(PicturePtr pict, int x, int y, int width, CARD32
             v.vector[2] += unit.vector[2];
         }
     }
+
+    fbFinishAccess (pict->pDrawable);
 }
 
 
@@ -3397,6 +3403,7 @@ static void fbStore(PicturePtr pict, int x, int y, int width, CARD32 *buffer)
 
     bits += y*stride;
     store(bits, buffer, x, width, indexed);
+    fbFinishAccess (pict->pDrawable);
 }
 
 static void fbStoreExternalAlpha(PicturePtr pict, int x, int y, int width, CARD32 *buffer)
@@ -3436,6 +3443,9 @@ static void fbStoreExternalAlpha(PicturePtr pict, int x, int y, int width, CARD3
 
     store(bits, buffer, x, width, indexed);
     astore(alpha_bits, buffer, ax - pict->alphaOrigin.x, width, aindexed);
+
+    fbFinishAccess (pict->alphaMap->pDrawable);
+    fbFinishAccess (pict->pDrawable);
 }
 
 typedef void (*scanStoreProc)(PicturePtr , int , int , int , CARD32 *);