AP_InertialSensor_MPU6000: Add _register_write_check method.

This private method allows to check whether the value written and
the posterior value readed are the same.
Should be used only for debuging purposes, for release versions use
_register_write instead.
Linux_HAL_Essentials: Update README for Ubuntu.

Added a note pointing out the instructions for precise.
HAL_Linux: Storage: Change storage folder in Linux to `/var/APM`
Linux_HAL_Essentials: Minor type fixed in the README
HAL_Linux: fixed SPI mode handling per-device

the mode must be set per-device, not per bus.
AP_InertialSensor: fixeup DRDY pin for different boards
HAL_Linux: MS5611 and MPU6000 should be MODE3

this doesn't solve the MPU6000 problem, but is correct
AP_InertialSensor: fixed DRDY include for Linux
HAL_Linux: added set_bus_speed() support to SPI driver

used by MPU6000 driver for setup registers
AP_InertialSensor_LSM9DS0: Remove previous CS handling.

CS is now being automatically handled by the SPI Driver.
AP_InertialSensor: added MPU9250 header
Copter: added support for MPU9250
AP_InertialSensor_LSM9DS0: Move LSM9DS0_DEBUG flag to the header
AP_InertialSensor_LSM9DS0: Fix _dump_registers method
HAL_Linux: fixed a build warning
HAL_Linux: fixed I2C driver build errors
AP_InertialSensor: fixed build errors for LSM9DSO
build: rename board_avr_sitl.mk to board_native.mk
build: added bbone as build target
Plane: enable MPU9250 for Linux build