x86_64: Add x86_64 syscalls and tune gen scripts for x86_64

x86_64: Add x86_64 syscalls and tune gen scripts for x86_64

* Tune syscall stubs generator for 4th target: x86_64
* Update SYSCALLS.TXT with x86_64 syscalls:
 - Most of the x86 syscalls are equally supported
 - *32 syscalls are not supported on 64-bit
 - *64 syscalls are replaced accordingly without 64 suffix
 - Some syscalls are not supported, replaced with x86_64 analog

Syscalls are regenerated as separate patch for review convenience.

Change-Id: I4ea2e0f13759b0aa61f05208ca68da8d6bc7c048
Signed-off-by: Pavel Chupin <pavel.v.chupin@intel.com>