boost: fix build on 64-bit target after bump to 1.54.0

Fixes compilation error with aarch64 target:

./boost/atomic/atomic.hpp: At global scope:
./boost/atomic/atomic.hpp:202:16: error: 'uintptr_t' was not declared in this scope
 typedef atomic<uintptr_t> atomic_uintptr_t;
                ^
./boost/atomic/atomic.hpp:202:25: error: template argument 1 is invalid
 typedef atomic<uintptr_t> atomic_uintptr_t;
                         ^
./boost/atomic/atomic.hpp:202:43: error: invalid type in declaration before ';' token
 typedef atomic<uintptr_t> atomic_uintptr_t;
                                           ^

Fixes http://autobuild.buildroot.net/results/0b69d7b33dc16ea27e395a949cefbd0a35c92f61/

Reported here: https://svn.boost.org/trac/boost/ticket/8973
Fix reported here: https://svn.boost.org/trac/boost/ticket/8731



Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Backported-from: https://svn.boost.org/trac/boost/changeset/84950


Signed-off-by: Peter Korsgaard <peter@korsgaard.com>