fbdev/logo: check compatibility of main and extra logos

The code to draw penguin logos always uses some properties of the main logo.
This is incorrect if additional logos (CONFIG_FB_LOGO_EXTRA=y) have different
types than the main logo, which causes corrupted logo images.

  http://bugzilla.kernel.org/show_bug.cgi?id=12181

Hence skip additional logos that are not compatible with the main logo.

Technically, it's possible to draw multiple logos of different types on
truecolor displays, but this would complicate the (already quite
complicated) logo drawing code even more.

This patch fixes a problem with Debian's linux-image-2.6.26-1-powerpc64
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=508173



Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>