fbdev/sisfb: Unexport symbols

fbdev/sisfb: Unexport symbols

Fix the compile-time warning

  drivers/video/fbdev/sis/sis_main.c: warning: EXPORT_SYMBOL() is used, but #include <linux/export.h> is missing

The affected symbols are not used outside of their module. Some of
the symbols are not used anywhere, so remove the functions entirely.
Also remove the related, but unused, define SISFB_HAVE_MALLOC_NEW.

v2:
- remove unused functions (Helge)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Helge Deller <deller@gmx.de>
Fixes: a934a57a42f6 ("scripts/misc-check: check missing #include <linux/export.h> when W=1")
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20250612081738.197826-13-tzimmermann@suse.de