Both the FFV1 decoder and encoder use a template of their own
to generate code multiple times. They also use a common template,
used by both decoder and encoder templates which is currently
instantiated in ffv1.h (and therefore also in ffv1.c, which
doesn't need it at all).

All these templates have the prerequisite that two macros
are defined, namely RENAME() and TYPE. The codec-specific
templates call the functions generated via the common template
via the RENAME() macro and therefore the macros used for
the common template must coincide with the macros used for
the codec-specific templates. But then it is better to not
instantiate the common template in ffv1.h, but in the codec
specific templates.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>