The x86/init/common/ folder holds all cpu initialization
code - idt and gdt setup, interrupts and cpu initialization.
On this folder will also sit any SoC specific implementation of
the functions called from cpu_init().
This patch adds code to initialize the Global Descriptor Table. For
simplicity, the memory is organized following the flat model. Thus,
memory appears to Contiki as a single, continuous address space. Code,
data, and stack are all contained in this address space (so called
linear address space).
The macros to manipulate bits from segment descriptor and the
set_descriptor() helper are based on the ones described in [1].
[1] http://wiki.osdev.org/GDT_Tutorial
