drivers: omap2: Kconfig: make FB_OMAP2_DSS_INIT depend on OF

Commit 7378f1149884 ("media: omap2: omapfb: allow building it with
COMPILE_TEST") broke compilation without CONFIG_OF selected.
CC drivers/video/fbdev/core/fbmem.o
drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c: In function ‘omapdss_update_prop’:
drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.c:68:2: error: implicit declaration of function ‘of_update_property’; did you mean ‘of_get_property’? [-Werror=implicit-function-declaration]
of_update_property(node, prop);
^~~~~~~~~~~~~~~~~~
of_get_property
cc1: some warnings being treated as errors
scripts/Makefile.build:312: recipe for target 'drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.o' failed
make[7]: *** [drivers/video/fbdev/omap2/omapfb/dss/omapdss-boot-init.o] Error 1
scripts/Makefile.build:559: recipe for target 'drivers/video/fbdev/omap2/omapfb/dss' failed
make[6]: *** [drivers/video/fbdev/omap2/omapfb/dss] Error 2
make[6]: *** Waiting for unfinished jobs....

Add OF dependency in order to make all configurations work again.

of_update_property() has no inline stub, and that that could be added as
an alternative.

Signed-off-by: Anders Roxell <[e-mail]>
Acked-by: Randy Dunlap <[e-mail]>
Tested-by: Randy Dunlap <[e-mail]>
Acked-by: Bartlomiej Zolnierkiewicz <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/video/fbdev/omap2/Kconfig

···
-if ARCH_OMAP2PLUS || COMPILE_TEST
+if OF && (ARCH_OMAP2PLUS || COMPILE_TEST)
 
 source "drivers/video/fbdev/omap2/omapfb/Kconfig"