Check bit "long mode active"

[maelgui]

While testing on baremetal, I encountered a bug in process_memio_op. An instruction was not decoded in the right mode. It seems to be a bug in mythil not checking the right bit in the field IA32_EFER of the vmcs. Bits "long mode enable" and especially "long mode active" must be checked. (see here https://wiki.osdev.org/CPU_Registers_x86-64#IA32_EFER)