MAINTAINERS: Add Borislav to the x86 maintainers

Borislav is effectivly maintaining parts of X86 already, make it official.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov <bp@alien8.de>

MAINTAINERS

@@ -15913,6 +15913,7 @@ F:	net/x25/
 X86 ARCHITECTURE (32-BIT AND 64-BIT)
 M:	Thomas Gleixner <tglx@linutronix.de>
 M:	Ingo Molnar <mingo@redhat.com>
+M:	Borislav Petkov <bp@alien8.de>
 R:	"H. Peter Anvin" <hpa@zytor.com>
 M:	x86@kernel.org
 L:	linux-kernel@vger.kernel.org