Kernel: Improve locking in Process, VFS and ATAController

We used to block on all process access. This meant that shell
reading the keyboard input would block all VFS access making disk
accesses practically impossible. We now block only when it is
necessary :)

kernel/include/kernel/Storage/ATAController.h

@@ -87,6 +87,7 @@ namespace Kernel
 	private:
 		ATABus m_buses[2];
 		const PCIDevice& m_pci_device;
+		SpinLock m_lock;
 
 		friend class ATADevice;