[PATCH -next] fbdev: offb: allow build when DRM_OFDRM=m

[Randy Dunlap <rdunlap@infradead.org>]

Fix build when CONFIG_FB_OF=y and CONFIG_DRM_OFDRM=m.
When the latter symbol is =m, kconfig downgrades (limits) the 'select's
under FB_OF to modular (=m). This causes undefined symbol references:

powerpc64-linux-ld: drivers/video/fbdev/offb.o:(.data.rel.ro+0x58): undefined reference to `cfb_fillrect'
powerpc64-linux-ld: drivers/video/fbdev/offb.o:(.data.rel.ro+0x60): undefined reference to `cfb_copyarea'
powerpc64-linux-ld: drivers/video/fbdev/offb.o:(.data.rel.ro+0x68): undefined reference to `cfb_imageblit'

Fix this by allowing FB_OF any time that DRM_OFDRM != y so that the
selected FB_CFB_* symbols will become =y instead of =m.

In tristate logic (for DRM_OFDRM), this changes the dependency from
    !DRM_OFDRM	== 2 - 1 == 1 => modular only (or disabled)
to (boolean)
    DRM_OFDRM != y == y, allowing the 'select's to cause the
FB_CFB_* symbols to =y instead of =m.

Fixes: c8a17756c425 ("drm/ofdrm: Add ofdrm for Open Firmware framebuffers")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Michal Suchánek <msuchanek@suse.de>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
---
 drivers/video/fbdev/Kconfig |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -- a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
--- a/drivers/video/fbdev/Kconfig
+++ b/drivers/video/fbdev/Kconfig
@@ -455,7 +455,7 @@ config FB_ATARI
 config FB_OF
 	bool "Open Firmware frame buffer device support"
 	depends on (FB = y) && PPC && (!PPC_PSERIES || PCI)
-	depends on !DRM_OFDRM
+	depends on DRM_OFDRM != y
 	select APERTURE_HELPERS
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA