[kernel] Clean up main.cpp and others

The kernel/main.cpp and kernel/memory_bootstrap.cpp files had become
something of a junk drawer. This change cleans them up in the following
ways:

- Most CPU initialization has moved to cpu.cpp, allowing several
  functions to be made static and removed from cpu.h
- Multi-core startup code has moved to the new smp.h and smp.cpp, and
  ap_startup.s has been renamed smp.s to match.
- run_constructors() has moved to memory_bootstrap.cpp, and all the
  functionality of that file has been hidden behind a new public
  interface mem::initialize().
- load_init_server() has moved from memory_bootstrap.cpp to main.cpp

src/kernel/interrupts.cpp

@@ -100,14 +100,14 @@ isr_handler(cpu_state *regs)
 
     case isr::isrGPFault:
         if (regs->errorcode & 0xfff0) {
-            int index = (regs->errorcode & 0xffff) >> 4;
+            int index = (regs->errorcode & 0xffff) >> 3;
             int ti = (regs->errorcode & 0x07) >> 1;
             char const *table =
                 (ti & 1) ? "IDT" :
                 (!ti) ? "GDT" :
                 "LDT";
 
-            snprintf(message, sizeof(message), "General Protection Fault, error:%lx%s %s[%d]",
+            snprintf(message, sizeof(message), "General Protection Fault, error:0x%lx%s %s[%d]",
                 regs->errorcode, regs->errorcode & 1 ? " external" : "", table, index);
         } else {
             snprintf(message, sizeof(message), "General Protection Fault, error:%lx%s",