Various accumulated x86-64 patches and bug fixes.

It fixes one nasty bug that has been there since NX is used by 
default in the kernel. With heavy AGP memory allocation it would
set NX on parts of the kernel mapping in some corner cases, which gave
endless crash loops. Thanks goes to some wizards in AMD debug labs
for getting a trace out of this.

Also various other fixes. This patches only changes x86-64 specific
files, i have some changes outside too that I am sending separately.

 - Fix help test for CONFIG_NUMA
 - Don't enable SMT nice on CMP
 - Move HT and MWAIT checks up to generic code
 - Update defconfig
 - Remove duplicated includes (Arthur Othieno)
 - Set up GSI entry for ACPI SCI correctly (from i386)
 - Fix some comments
 - Fix threadinfo printing in oopses
 - Set task alignment to 16 bytes
 - Handle NX bit for code pages correctly in change_page_attr()
 - Use generic nops for non amd specific kernel
 - Add __KERNEL__ checks in unistd.h (David Lee)