AP_HAL: Add SPIDevice_MPU9250 as a device.
AP_HAL_Linux: Add support for SPIDevice_MPU9250

The Invensense MPU9250 SPI device is connected to
SPI1, thereby SPIDriver class should return the
corresponding device.
AP_InertialSensor_MPU9250: SPI userspace sensor driver.

InvenSense MPU9250 sensor driver and test code (available under
libraries/examples/).
AP_HAL_Linux_Class: Correct deadlock, and infinite loop in setup()

(credit to Mitch Miers <mmiers@mmiers.com>):

setup() is attempting to initialize the hardware, and while doing so
is attempting to output some text via the console (and maybe mavlink
data).  The problem is, the output isn't going to complete once a
write buffer is full, because LinuxUARTDriver::_timer_tick() doesn't
perform work until _initialized is true.  So, what happens is,
setup() (and subroutines) call LinuxUARTDriver::_write(uint8_t c),
which loops waiting for buffer space to become available (once the
write buffer is full).  The buffer never gets space, because the
UART thread is waiting for initialization to complete before it
will write out data and drain the buffer, but that doesn't happen
until setup() returns (see AP_HAL_Linux_main.h).

Refer to https://groups.google.com/forum/#!topic/beaglepilot/dQlxse11JNI
AP_Baro_MS5611: Fix the test code so that compiles.

Add HAL_BOARD_LINUX and HAL_BOARD_ERLE compatibility.
AP_InertialSensor_MPU6000: Fix the test code so that compiles.
AP_InertialSensor_MPU9150: Comment the suspend_timer_procs

It causes the driver to hang. This matter should be inspected.
AP_HAL_Linux: Add support for SPIDevice_MS5611
Add initial RCOutput driver to AP_HAL_Linux
The functions in RCOutput.cpp are defined to access PWM over PRU sysfs device from userspace using open, read, write and close methods.
Create Readme.md adding details on manually testing pru pwm
Add Steps to Manually test pwm channels
HAL_Linux: Correct Indentation issue
HAL_Linux: Correct indentation
HAL_Linux: Correct faulty RCOutput driver

solve compiler not looking ahead of RCOutput class for read and write methods
HAL_Linux: add rcout->init method to HAL_Linux_Class::init method
HAL_Linux: add rcout->init method to HAL_Linux_Class::init
HAL_Linux: correct AP_HAL_Linux::RCOutput::enable_ch method

change the mode of file open which was set as RDONLY mistakenly
AP_InertialSensor_LSM9DS0: SPI userspace sensor driver.

ST Microelectronics 9 DOF IMU userspace sensor driver. Some
work with the filters needs to be done.
AP_HAL_Linux: Add support for SPIDevice_LSM9DS0

The LSM9DS0 SPI device is connected to
SPI0, thereby SPIDriver class should return the
corresponding device.
AP_InertialSensor_MPU9150: Clock-based wait_for_sample() impl.

Adapt the I2C driver to a system clock based wait_for_sample()
implementation.

The sample rate of the sensor has been corrected to 800 Hz (could be
further pushed up to 1KHz).

Filters for the mag have also been created but remain commented until
the code for the mag is ready.