fbdev: detect primary display device

Add function helper, fb_is_primary_device().  Given struct fb_info, it will
return a nonzero value if the device is the primary display.

Currently, only the i386 is supported where the function checks for the
IORESOURCE_ROM_SHADOW flag.

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/i386/video/Makefile b/arch/i386/video/Makefile
new file mode 100644
index 0000000..2c447c9
--- /dev/null
+++ b/arch/i386/video/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_FB)               += fbdev.o