x86_64 port and BSP (GSoC 2018)

[Amaan Cheval]

Status update time!

# Completed:
[x] Get my QEMU environment setup
     - Documented on the RTEMS wiki[1]
[x] Read more of RTEMS' no_cpu code, and the BSP porting guide
     - Read most of the guide - things have been in flux with the
refactorings, but I think most of it makes sense, especially after having
found the tickets on Trac - the reorganization of folders (to bsps from all
over) and simplified build systems are helping make it easier to understand
for sure. I haven't quite figured out what initialization happens where
since we have a fair number of "init" spots and the delineation isn't
crystal clear yet, but I'll ask about that if I don't figure it out soon.
(In particular, we've got start.S for boot, boot_card, _CPU_Initialize,
etc. - I'll likely know soon enough from looking at other architectures.)

# In progress:
[-] Create a stub port and BSP simply to link with testsuite, as Joel
suggested to surface any issues with the tools.
     - I simply copied no_cpu and parts of i386 into x86_64 directory,
updated "/c/src/aclocal/rtems-cpu-subdirs.m4" and off I went.
     - Would we be interested in patches to update no_bsp to make this "port
by starting from no_bsp" method easier? For eg. interrupts.h doesn't exist
in no_bsp, but is assumed in other parts of RTEMS.
I imagine we'll also want no_cpu to be reorganized into the root "bsps"
folder (per ticket #3285) to be the go-to reference structure for a new
port, so these patches may be better after that does happen to avoid
conflicts. (I already sent a patch for a fairly simple issue here[2], but
let me know if you'd rather have the others after the reorganization or now
- I haven't started work on them per-se, only as a byproduct of trying to
get the stub x86_64 port to compile.)
     - I ran into an issue (seems minor) with the x86_64 tools (gcc);
thought I'd put that in its own thread[3], since not everyone may be
interested in this status update.

[-] Continue to read Intel's manual on system programming (volume 3)
     - In progress - there's a lot, so I'm skimming a fair bit, looking for
key things that I may not have accounted for.

# Incomplete:
[ ] Read / skim FreeBSD's code for UEFI, APIC support, SMP, etc.
     - Doing this as soon as I've made enough progress on the stub port
mentioned above.
[ ] Read / skim UEFI specification
[ ] Figure out how testing on community hardware


[1]
https://devel.rtems.org/wiki/Developer/Simulators/QEMU#QEMUandUEFIusingOVMFEDKII
[2] https://lists.rtems.org/pipermail/devel/2018-April/020857.html
[3] https://lists.rtems.org/pipermail/devel/2018-April/020858.html