xfree86: Prealloacte morespace to mittigate invalid pointer issues after table reallocation
There are rare cases(#910 (closed)) when xf86SetDepthBpp is resizing displays array in confScreen. As that array is shared between set of ScrnInfoRec's then realloc might invalidate chached DispPtr display values in otheres ScrnInfoRec objects.
If we pre-allocate more space then necessary then a chance of need to reallocate will be minimized.
This is not ideal solution which is basing on assumption that reallocation won't happen as there is small chance of having more than 10 display config sections but it is still better than random crash on device plug in.