omapfb: rename omap2 module to omap2fb.ko

In a kernel configuration with both CONFIG_FB_OMAP=m and CONFIG_FB_OMAP2=m,
Kbuild fails to point out that we have two modules with the same name (omapfb.ko),
but instead fails with a cryptic error message like:

ERROR: "omapfb_register_panel" [drivers/video/fbdev/omap/lcd_osk.ko] undefined!

This can now happen when building a randconfig kernel with CONFIG_ARCH_OMAP1,
as the omap1 fbdev driver depends on that, whiel the omap2 fbdev driver can
now be built anywhere with CONFIG_COMPILE_TEST.

The solution is to rename one of the two modules, so for consistency with
the directory naming I decided to rename the omap2 version to omap2fb.ko.

Fixes: 7378f1149884 ("media: omap2: omapfb: allow building it with COMPILE_TEST")
Signed-off-by: Arnd Bergmann <[e-mail]>
Acked-by: Tony Lindgren <[e-mail]>
Cc: Mauro Carvalho Chehab <[e-mail]>
Signed-off-by: Bartlomiej Zolnierkiewicz <[e-mail]>

drivers/video/fbdev/omap2/omapfb/Makefile

···
 obj-$(CONFIG_OMAP2_VRFB) += vrfb.o
 obj-y += dss/
 obj-y += displays/
-obj-$(CONFIG_FB_OMAP2) += omapfb.o
-omapfb-y := omapfb-main.o omapfb-sysfs.o omapfb-ioctl.o
+obj-$(CONFIG_FB_OMAP2) += omap2fb.o
+omap2fb-y := omapfb-main.o omapfb-sysfs.o omapfb-ioctl.o