fbdev: work around old compiler bug

When building with a 4.1.x compiler on powerpc64 (at least) we get this
error:

drivers/video/logo/logo_linux_mono.c:81: error: logo_linux_mono causes a section type conflict

This was introduced by commit ae52bb2384f721562f15f719de1acb8e934733cb
("fbdev: move logo externs to header file").  This is a partial revert of
that commit sufficient to not hit the compiler bug.

Also convert _clut arrays from __initconst to __initdata.

Sam said:

  Al analysed this some time ago.  When we say something is const then
  _sometimes_ gcc annotate the section as const(?) - sometimes not.  So if
  we have two variables/functions annotated __*const and gcc decides to
  annotate the section const only in one case we get a section type
  conflict.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Cc: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Cc: Kyle McMartin <kyle@mcmartin.ca>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>