clean-up left-over arch-depend code from kernel base

clean-up left-over arch-depend code from kernel base

* ref: restructure the trace related arch-dependent stuff to make it
       less redundant
* ref: rename the boot_end/boot_start section markers so it will not
       conflict with out in name (in particular the boot_end() function)
* ref: remove the reference to port-io thing from ahci driver base
* ref: only compile the pmio vairant of uart when the correspond,
  arch-related feature is turned on.
* ref: temporary disable the vga module, as it is incompleted and buggy
* fix: add back a missing #include to asm/cpu.h