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: 7378f114 ("media: omap2: omapfb: allow building it with COMPILE_TEST")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Tony Lindgren <tony@atomide.com>
Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>