[BLOCK] Move all core block layer code to new block/ directory

drivers/block/ is right now a mix of core and driver parts. Lets move
the core parts to a new top level directory. Al will move the fs/
related block parts to block/ next.

Signed-off-by: Jens Axboe <axboe@suse.de>
diff --git a/init/Kconfig b/init/Kconfig
index 3dcbd5b..ea097e0 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -501,3 +501,7 @@
 	help
 	  Need stop_machine() primitive.
 endmenu
+
+menu "Block layer"
+source "block/Kconfig"
+endmenu