Kernel: Implement a simple Scatter/Gather List

This allows converting a single virtual buffer into its non-physically
contiguous parts, this is especially useful for DMA-based devices that
support scatter/gather-like functionality, as it eliminates the need
to clone outgoing buffers into one physically contiguous buffer.

Kernel/CMakeLists.txt

@@ -236,6 +236,7 @@ set(KERNEL_SOURCES
     VM/Range.cpp
     VM/RangeAllocator.cpp
     VM/Region.cpp
+    VM/ScatterGatherList.cpp
     VM/SharedInodeVMObject.cpp
     VM/Space.cpp
     VM/VMObject.cpp