tune: Remove tune-x86_64.inc

tune: Remove tune-x86_64.inc

The tune-x86_64.inc file is conceptually flawed. x86_64 is more akin to
the x86 and x86-32 ABIs defined in arch-x86.inc than it is a concrete
tune file, such as i586 or core2 - to the extent that everything but the
default tune is defined in the arch-x86.inc file. This becomes very
apparant when attempting to include tune-x86_64.inc in the x86 tune
hierarchy.

Remove the tune-x86_64.inc tune file in favor of it being an ABI
definition in arch-x86.inc and relying on the linear hierarchy of
concrete cpu-types in tune-i586, tune-core2, and tune-corei7.

core2_64 should suffice in lieu of x86_64 for all but a couple esoteric
corner cases involving older pre-core2 CPUs. In these cases, if they
exist at all, the BSP can replace the include tune-x86_64.inc with
arch-x86.inc and set the default tune to x86_64.

(From OE-Core rev: d8884649b2b3e76519bc10f5908f98d940a9c0cb)

Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
Cc: Paul Eggleton <paul.eggleton@intel.com>
Cc: Tom Zanussi <tom.zanussi@intel.com>
Cc: Nitin Kamble <nitin.a.kamble@intel.com>
Cc: Mark Hatle <mark.hatle@windriver.com>
Cc: Bruce Ashfield <bruce.ashfield@windriver.com>
Cc: Martin Jansa <martin.jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>