[U-Boot] Swig now required to build U-Boot?

[Stephen Warren]

Simon,

Is it expected that the latest u-boot-dm.git master branch now requires 
swig? All the non-sandbox builds on my test systems are failing:

   CHK     include/config/uboot.release
   CHK     include/generated/timestamp_autogenerated.h
   GEN     ./Makefile
   UPD     include/generated/timestamp_autogenerated.h
   CHK     include/config.h
   CFG     u-boot.cfg
   SHIPPED scripts/dtc/pylibfdt/libfdt.i
   PYMOD   scripts/dtc/pylibfdt/_libfdt.so
unable to execute 'swig': No such file or directory
error: command 'swig' failed with exit status 1
make[4]: *** [scripts/dtc/pylibfdt/_libfdt.so] Error 1
make[3]: *** [scripts/dtc/pylibfdt] Error 2
make[2]: *** [scripts/dtc] Error 2
make[1]: *** [scripts] Error 2
make[1]: *** Waiting for unfinished jobs....