um: remove redundant generic-y

This commit removes redundant generic-y defines in
arch/um/include/asm/Kbuild.

It is redundant to define generic-y when arch-specific implementation
exists in arch/$(ARCH)/include/asm/*.h

Remove the following generic-y:

    hardirq.h
    io.h
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/include/asm/Kbuild

@@ -10,9 +10,7 @@ generic-y += exec.h
 generic-y += extable.h
 generic-y += ftrace.h
 generic-y += futex.h
-generic-y += hardirq.h
 generic-y += hw_irq.h
-generic-y += io.h
 generic-y += irq_regs.h
 generic-y += irq_work.h
 generic-y += kdebug.h