Remove useless wrappers of asm-generic/ipc.h

mn10300 has a header (in its include/asm directory) that is a thin
wrapper around asm-generic/ipc.h. This wrapper is useless, since that
header doesn't exist. It is also unused (no file includes asm/ipc.h).

hexagon and tile generate similar headers at build time (using a
generic-y entry in include/asm/Kbuild). These generated headers are
useless and unused too.

Remove this header and these generic-y entries.

Signed-off-by: Paul Bolle <[e-mail]>
Acked-by: Richard Kuo <[e-mail]>
Acked-by: Chris Metcalf <[e-mail]>
Acked-by: David Howells <[e-mail]> [MN10300]
Signed-off-by: Michal Marek <[e-mail]>

arch/hexagon/include/asm/Kbuild

···
 generic-y += ioctls.h
 generic-y += iomap.h
 generic-y += ipcbuf.h
-generic-y += ipc.h
 generic-y += irq_regs.h
 generic-y += kdebug.h
 generic-y += kmap_types.h

arch/mn10300/include/asm/ipc.h

···
-#include <asm-generic/ipc.h>

arch/tile/include/asm/Kbuild

···
 generic-y += fcntl.h
 generic-y += ioctl.h
 generic-y += ioctls.h
-generic-y += ipc.h
 generic-y += ipcbuf.h
 generic-y += irq_regs.h
 generic-y += kdebug.h