cmake: param refactoring

Use a struct to contain all the parameters so the ordering in
memory is not machine dependent.

Add number of parameters to the param struct. The struct actually
allows direct accessing by the member name if desired.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/firmware/posix/CMakeLists.txt

@@ -9,7 +9,7 @@ px4_generate_parameters()
 
 add_executable(mainapp
 	${CMAKE_SOURCE_DIR}/src/platforms/posix/main.cpp
-	${CMAKE_BINARY_DIR}/parameters.c
+	${CMAKE_BINARY_DIR}/px4_parameters.c
 	apps.h
 	)