this should allow us to work even with older chips. See the MPU6000
product specification, which says max 20MHz for sensor and interrupt
regs, and max 1MHz for all other regs
We now init the MPU6k CS pin before the MS5611 CS pin. This should not
matter at all, but it turns out that it solves the APM2 boot
problem. We should investigate why, as this may indicate an electrical
problem.
Pair-Programmed-With: Pat Hickey