hmc5983: add driver for hmc5983 magnetometer
ms5611: add driver for ms5611 pressure sensor attached to SPI
systemmod: allow systemmod to build without i2c
ms5611_spi: fix coding style violations
hmc5983: fix coding style violations
pios.h: fix coding style violations
Merge pull request #689 from solidgoldbomb/rescue-trollcop-drivers

Rescue trollcop drivers