turbostat: Don't put unprocessed uapi headers in the include path

turbostat's Makefile puts arch/x86/include/uapi/ in the include path, so
that it can include <asm/msr.h> from it.  It isn't in general safe to
include even uapi headers directly from the kernel tree without
processing them through scripts/headers_install.sh, but asm/msr.h
happens to work.

However, that include path can break with some versions of system
headers, by overriding some system headers with the unprocessed versions
directly from the kernel source.  For instance:

In file included from /build/x86-generic/usr/include/bits/sigcontext.h:28:0,
                 from /build/x86-generic/usr/include/signal.h:339,
                 from /build/x86-generic/usr/include/sys/wait.h:31,
                 from turbostat.c:27:
../../../../arch/x86/include/uapi/asm/sigcontext.h:4:28: fatal error: linux/compiler.h: No such file or directory

This occurs because the system bits/sigcontext.h on that build system
includes <asm/sigcontext.h>, and asm/sigcontext.h in the kernel source
includes <linux/compiler.h>, which scripts/headers_install.sh would have
filtered out.

Since turbostat really only wants a single header, just include that one
header rather than putting an entire directory of kernel headers on the
include path.

In the process, switch from msr.h to msr-index.h, since turbostat just
wants the MSR numbers.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Cc: stable@vger.kernel.org
Signed-off-by: Len Brown <len.brown@intel.com>