Capability checking added as compiling code.

Capability checking for thread_control, exregs, mutex, cap_control,
ipc, and map system calls.

The visualised model is implemented in code that compiles, but
actual functionality hasn't been tested.

Need to add:
- Dynamic assignment of initial resources matching with what's
defined in the configuration.
- A paged-thread-group, since that would be a logical group of
seperation from a capability point-of-view.
- Resource ids for various tasks. E.g.
  - Memory capabilities don't have target resources.
  - Thread capability assumes current container for THREAD_CREATE.
  - Mutex syscall assumes current thread (this one may not need
    any changing)
  - cap_control syscall assumes current thread. It may happen to
    be that another thread's capability list is manipulated.

Last but not least:
- A simple and easy-to-use userspace library for dynamic expansion
  of resource domains as new resources are created such as threads.

include/l4/api/exregs.h

@@ -13,6 +13,27 @@
 
 #define EXREGS_SET_PAGER		1
 #define	EXREGS_SET_UTCB			2
+#define EXREGS_VALID_REGULAR_REGS 			\
+	(FIELD_TO_BIT(exregs_context_t, r0) |		\
+	 FIELD_TO_BIT(exregs_context_t, r1) |		\
+	 FIELD_TO_BIT(exregs_context_t, r2) |		\
+	 FIELD_TO_BIT(exregs_context_t, r3) |		\
+	 FIELD_TO_BIT(exregs_context_t, r4) |		\
+	 FIELD_TO_BIT(exregs_context_t, r5) |		\
+	 FIELD_TO_BIT(exregs_context_t, r6) |		\
+	 FIELD_TO_BIT(exregs_context_t, r7) |		\
+	 FIELD_TO_BIT(exregs_context_t, r8) |		\
+	 FIELD_TO_BIT(exregs_context_t, r9) |		\
+	 FIELD_TO_BIT(exregs_context_t, r10) |		\
+	 FIELD_TO_BIT(exregs_context_t, r11) |		\
+	 FIELD_TO_BIT(exregs_context_t, r12) |		\
+	 FIELD_TO_BIT(exregs_context_t, lr))		\
+
+#define EXREGS_VALID_SP 				\
+	FIELD_TO_BIT(exregs_context_t, sp)		\
+
+#define EXREGS_VALID_PC 				\
+	FIELD_TO_BIT(exregs_context_t, pc)		\
 
 /* Structure passed by userspace pagers for exchanging registers */
 struct exregs_data {