efi: Move efifb_setup_from_dmi() prototype from arch headers

efi: Move efifb_setup_from_dmi() prototype from arch headers

Commit 8633ef82f101 ("drivers/firmware: consolidate EFI framebuffer setup
for all arches") made the Generic System Framebuffers (sysfb) driver able
to be built on non-x86 architectures.

But it left the efifb_setup_from_dmi() function prototype declaration in
the architecture specific headers. This could lead to the following
compiler warning as reported by the kernel test robot:

   drivers/firmware/efi/sysfb_efi.c:70:6: warning: no previous prototype for function 'efifb_setup_from_dmi' [-Wmissing-prototypes]
   void efifb_setup_from_dmi(struct screen_info *si, const char *opt)
        ^
   drivers/firmware/efi/sysfb_efi.c:70:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   void efifb_setup_from_dmi(struct screen_info *si, const char *opt)

Fixes: 8633ef82f101 ("drivers/firmware: consolidate EFI framebuffer setup for all arches")
Reported-by: kernel test robot <lkp@intel.com>
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20211126001333.555514-1-javierm@redhat.com
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>