hw/sensor: Add lsm303dlhc magnetometer device

This commit adds emulation of the magnetometer on the LSM303DLHC.
It allows the magnetometer's X, Y and Z outputs to be set via the
mag-x, mag-y and mag-z properties, as well as the 12-bit
temperature output via the temperature property. Sensor can be
enabled with 'CONFIG_LSM303DLHC_MAG=y'.

Signed-off-by: Kevin Townsend <kevin.townsend@linaro.org>
Message-id: 20220130095032.35392-1-kevin.townsend@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>