hikey: do not call hisi-idt.py with hardcoded python command

Let hisi-idt.py decide which python interpreter is used based on the
hashbang line. Calling "python" can cause compatibility problems when
"python" is Python 2 but the script needs Python3.

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>