platform/stm32-e407/mkhalh (delay_us): convert to proper delay loop (48 MHz)
platform/stm32-e407/rtimer-arch.c: copy over from stm32ldiscovery
platform/stm32-e407/rtimer-arch.c (rtimer_arch_init): comment out for now

This doesn't look as if it would be easy to port from 32L to 32F4.
Luckily, it seems that we can do without it for now.
enable serial input, switch from blipper to serial-shell, and enable some networking
platform/stm32-e407/contiki-main.c: don't call hal_test

We don't need it anymore at this point. May still be handy for testing
new hardware, though.