Kernel: Implement proper memory region splitting

Memory regions are now splitted when they get munmapped, mprotected, or
mmapped with MAP_FIXED. This is used by couple of ports, and without
this we were just leaking up memory or straight up crashing programs.

kernel/kernel/Device/FramebufferDevice.cpp

@@ -301,6 +301,13 @@ namespace Kernel
 			return BAN::UniqPtr<MemoryRegion>(BAN::move(region));
 		}
 
+		BAN::ErrorOr<BAN::UniqPtr<MemoryRegion>> split(size_t offset) override
+		{
+			(void)offset;
+			dwarnln("TODO: FramebufferMemoryRegion::split");
+			return BAN::Error::from_errno(ENOTSUP);
+		}
+
 	protected:
 		// Returns error if no memory was available
 		// Returns true if page was succesfully allocated