selftests/x86/corrupt_xstate_header: Use provided __cpuid_count() macro

selftests/x86/corrupt_xstate_header: Use provided __cpuid_count() macro

kselftest.h makes the __cpuid_count() macro available
to conveniently call the CPUID instruction.

Remove the local CPUID wrapper and use __cpuid_count()
from kselftest.h instead.

__cpuid_count() from kselftest.h is used instead of the
macro provided by the compiler since gcc v4.4 (via cpuid.h)
because the selftest needs to be supported with gcc v3.2,
the minimal required version for stable kernels.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>