What is the point in surrounding the whole of declarations with
ifdef like this?

  #ifdef CONFIG_FOO
  int foo(void);
  #endif

If CONFIG_FOO is not defined, all callers of foo() will fail
with implicit declaration errors since the top Makefile adds
-Werror-implicit-function-declaration to KBUILD_CFLAGS.

This breaks the build earlier when you are doing something wrong.
That's it.

Anyway, it will fail to link since the definition of foo() is not
compiled.

In summary, these ifdef are unneeded.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>