x86/pconfig: Detect PCONFIG targets

Intel PCONFIG targets are enumerated via new CPUID leaf 0x1b. This patch
detects all supported targets of PCONFIG and implements helper to check
if the target is supported.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Kai Huang <kai.huang@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180305162610.37510-5-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>