sparc: Fix undefined reference to fb_is_primary_device

Commit 55bffc81 ("fbdev: Split frame buffer support in FB and FB_CORE
symbols") added a new FB_CORE Kconfig symbol, that can be enabled to only
have fbcon/VT and DRM fbdev emulation, but without support for any legacy
fbdev driver.

Unfortunately, it missed to change the CONFIG_FB in arch/sparc makefiles,
which leads to the following linking error in some sparc64 configurations:

   sparc64-linux-ld: drivers/video/fbdev/core/fbcon.o: in function `fbcon_fb_registered':
>> fbcon.c:(.text+0x4f60): undefined reference to `fb_is_primary_device'

Fixes: 55bffc81 ("fbdev: Split frame buffer support in FB and FB_CORE symbols")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/r/202401290306.IV8rhJ02-lkp@intel.com/


Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: <stable@vger.kernel.org> # v6.6+
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240220095428.3341195-1-javierm@redhat.com