libfreeimage: disable on ARC and Blackfin

libfreeimage fails to build on ARC, due to compiler issues:

  Error: invalid register number `63'

This should probably be fixed at the compiler level.

It also fails to build on Blackfin, due to numerous libfreeimage
issues:

  1/ Missing LL suffixes in Source/OpenEXR/IlmImf/ImfFastHuf.cpp. This
     can be fixed by backporting upstream OpenEXR commit
     https://github.com/openexr/openexr/commit/57ecf581d053f5cacf2e8fc3c024490e0bbe536f.patch.

  2/ Invalid characters in libraw_x3f.cpp. This can be fixed by
     applying dos2unix on the file.

  3/ Usage of too long constants in an unsigned long in
     dcraw_common.cpp, in code like "id == 0x4434303430" where id is
     an "unsigned long" i.e 32 bits on 32 bits platform.

Due to (3) being apparently unsolved upstream, and causing a build
error on Blackfin, we disable libfreeimage on this
architecture. However, this code seems so broken that making
libfreeimage as entirely broken would maybe be a better option.

Fixes:

  http://autobuild.buildroot.org/results/b33/b3372581c82786cc0a87f8cc2e78f047cc079255/ (ARC issue)
  http://autobuild.buildroot.org/results/f3b/f3bd6be448cffed3caae7850233168e6d0f6a5bd/

 (Blackfin issue)

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>