BMI270 acc support

Just the accelerometer for now.

It doesn't implement its own data retrieval task, so calling it from Python is a synchronous I2C transaction. Can be optimized later.

components/bmi270/CMakeLists.txt

+idf_component_register(
+    SRCS
+        bmi270.c
+        bmi2.c
+    INCLUDE_DIRS
+        .
+)