[kernel] Move log buffer to its own memory section

In prep for the coming change to keep log entries as a true ring buffer,
move the log buffer from bss into its own memory section.

Related changes in this commit:
- New vm_area_ring, which maps a set of pages twice to allow easy linear
  reading of data from a ring buffer when it wraps around the end.
- logger_init() went away, and the logger ctor is called from
  mem::initialize()
- Instead of an event object, the logger just has a bare wait_queue
- util::counted::from template type changed slightly to allow easy
  conversion from an intptr_t as well as a pointer
- Previously added debugcon_logger code removed - this will be added in
  a separate file in a followup commit

src/libraries/util/util/counted.h

@@ -70,7 +70,7 @@ struct counted<const void>
     size_t count = 0;
 
     template <typename T>
-    static inline counted<const void> from(T *p, size_t c) {
+    static inline counted<const void> from(T p, size_t c) {
         return {reinterpret_cast<const void*>(p), c};
     }
 
@@ -108,7 +108,7 @@ struct counted<void>
     size_t count = 0;
 
     template <typename T>
-    static inline counted<void> from(T *p, size_t c) {
+    static inline counted<void> from(T p, size_t c) {
         return {reinterpret_cast<void*>(p), c};
     }