[MIPS] Have headers_install install <asm/cachectl.h> and <asm/sysmips.h>.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

include/asm-mips/Kbuild

@@ -1,3 +1,3 @@
 include include/asm-generic/Kbuild.asm
 
-header-y += sgidefs.h
+header-y += cachectl.h sgidefs.h sysmips.h