cyclic: introduce u-boot/schedule.h

cyclic: introduce u-boot/schedule.h

I noticed an "unnecessary" include of <cyclic.h> in
global_data.h, in the sense that nothing in cyclic.h is needed in
order to define 'struct global_data'.

Well, it's not unnecessary, as it implicitly ensures that everybody
gets a declaration of schedule(), and schedule() is (obviously) called
all over the tree. Almost none of those places directly include
<cyclic.h>, but for historical reasons, many do include
<watchdog.h> (most schedule() instances are replacements of
WATCHDOG_RESET()).

However, very few TUs actually need the declarations of the
cyclic_register() and struct cyclic_info, and they also don't really
need anything from the watchdog.h header.

So introduce a new header which just contains a declaration of
schedule(), which can then be included from all the places that do
call schedule(). I removed the direct reference to cyclic_run(),
because we shouldn't have two public functions for doing roughly the
same without being very explicit about when one should call one or the
other.

Testing of later patches that explicitly include <schedule.h> when
schedule() is used revealed a problem with host tool build on win32,
which apparently picked up a host <schedule.h>. To avoid that problem,
put the new header in include/u-boot/ and hence make the include
statements say <u-boot/schedule.h>.

Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>