iio:imu:mpu6050: enhance mounting matrix support

Add a new rotation matrix sysfs attribute compliant with IIO core
mounting matrix API.
Matrix is retrieved from "in_anglvel_mount_matrix" and
"in_accel_mount_matrix" sysfs attributes. It is declared into mpu6050 DTS
entry as a "mount-matrix" property.

Old interface is kept for backward userspace compatibility and may be
retrieved from legacy platform_data mechanism only.

Signed-off-by: Gregor Boirie <gregor.boirie@parrot.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/include/linux/platform_data/invensense_mpu6050.h b/include/linux/platform_data/invensense_mpu6050.h
index ad3aa7b..554b598 100644
--- a/include/linux/platform_data/invensense_mpu6050.h
+++ b/include/linux/platform_data/invensense_mpu6050.h
@@ -16,13 +16,16 @@
 
 /**
  * struct inv_mpu6050_platform_data - Platform data for the mpu driver
- * @orientation:	Orientation matrix of the chip
+ * @orientation:	Orientation matrix of the chip (deprecated in favor of
+ *			mounting matrix retrieved from device-tree)
  *
  * Contains platform specific information on how to configure the MPU6050 to
  * work on this platform.  The orientation matricies are 3x3 rotation matricies
  * that are applied to the data to rotate from the mounting orientation to the
  * platform orientation.  The values must be one of 0, 1, or -1 and each row and
  * column should have exactly 1 non-zero value.
+ *
+ * Deprecated in favor of mounting matrix retrieved from device-tree.
  */
 struct inv_mpu6050_platform_data {
 	__s8 orientation[9];