Add generic Kbuild files for 'make headers_install'

This adds the Kbuild files listing the files which are to be installed by
the 'headers_install' make target, in generic directories.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
diff --git a/include/mtd/Kbuild b/include/mtd/Kbuild
new file mode 100644
index 0000000..e1da2a5
--- /dev/null
+++ b/include/mtd/Kbuild
@@ -0,0 +1,2 @@
+unifdef-y := mtd-abi.h
+header-y := inftl-user.h jffs2-user.h mtd-user.h nftl-user.h