fbdev: fbmem: convert CONFIG_FB_LOGO_CENTER into a cmd line option

A command line option is much more flexible than a config option and
the supporting code is small. Gets rid of #ifdefs in the code too...

Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>