python: build host-python with MAKE1

Building host-python in parallel sometimes causes "Bus error" during
the installation step on our autobuilders, such as:

  http://autobuild.buildroot.org/results/04bcc907c5e075fe1f39d4f49dcc50ec93708eb4/build-end.log



Extensive testing on one autobuilder has shown that building
host-python with MAKE1 work arounds this strange problem.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>