[kernel] Pass objects not handles to syscall impls

This commit contains a couple large, interdependent changes:

- In preparation for capability checking, the _syscall_verify_*
  functions now load most handles passed in, and verify that they exist
  and are of the correct type. Lists and out-handles are not converted
  to objects.
- Also in preparation for capability checking, the internal
  representation of handles has changed. j6_handle_t is now 32 bits, and
  a new j6_cap_t (also 32 bits) is added. Handles of a process are now a
  util::map<j6_handle_t, handle> where handle is a new struct containing
  the id, capabilities, and object pointer.
- The kernel object definition DSL gained a few changes to support auto
  generating the handle -> object conversion in the _syscall_verify_*
  functions, mostly knowing the object type, and an optional "cname"
  attribute on objects where their names differ from C++ code.
  (Specifically vma/vm_area)
- Kernel object code and other code under kernel/objects is now in a new
  obj:: namespace, because fuck you <cstdlib> for putting "system" in
  the global namespace. Why even have that header then?
- Kernel object types constructed with the construct_handle helper now
  have a creation_caps static member to declare what capabilities a
  newly created object's handle should have.

src/kernel/device_manager.h

@@ -10,7 +10,10 @@
 
 struct acpi_table_header;
 class block_device;
-class endpoint;
+
+namespace obj {
+    class endpoint;
+}
 
 using irq_callback = void (*)(void *);
 
@@ -43,11 +46,11 @@ public:
     /// \arg irq    The IRQ number to bind
     /// \arg target The endpoint to recieve messages when the IRQ is signalled
     /// \returns    True on success
-    bool bind_irq(unsigned irq, endpoint *target);
+    bool bind_irq(unsigned irq, obj::endpoint *target);
 
     /// Remove IRQ bindings for an endpoint
     /// \arg target The endpoint to remove
-    void unbind_irqs(endpoint *target);
+    void unbind_irqs(obj::endpoint *target);
 
     /// Allocate an MSI IRQ for a device
     /// \arg name    Name of the interrupt, for display to user
@@ -161,7 +164,7 @@ private:
     util::vector<pci_group> m_pci;
     util::vector<pci_device> m_devices;
 
-    util::vector<endpoint*> m_irqs;
+    util::vector<obj::endpoint*> m_irqs;
 
     util::vector<block_device *> m_blockdevs;