drm/i915/fbdev: fix link failure without FBDEV emulation

drm/i915/fbdev: fix link failure without FBDEV emulation

If CONFIG_DRM_FBDEV_EMULATION is disabled but CONFIG_FRAMEBUFFER_CONSOLE
is turned on, the i915 driver now fails to link:

ERROR: modpost: "intel_fbdev_fb_prefer_stolen" [drivers/gpu/drm/i915/i915.ko] undefined!

Fix the contition to include a check for the symbol that controls compilation
of intel_fbdev_fb.c.

Fixes: 94c7d2861292 ("drm/i915/fbdev: Extract intel_fbdev_fb_prefer_stolen()")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20260304083701.724908-1-arnd@kernel.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>