ARM: boot0 hook: remove macro, include whole header file

For prepending some board specific header area to U-Boot images we
were so far including a header file with a macro definition containing
the actual header specification.
This works fine if there are just a few statements and if there is only
one alternative.
However adding more complex code quickly gets messy with this approach,
so let's just drop that intermediate macro and let the #include actually
insert the code directly.
This converts the callers and the callees, but doesn't change anything
at this point.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Steve Rae <steve.rae@raedomain.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>