Explicitly specify ADIOS2 components in openPMDConfig.cmake

When including openPMD in downstream CMake and that CMake script
contains Fortran, ADIOS2 will automatically detect that. But since we
do not reexport the ADIOS2 headers, we only need the components that
openPMD explicitly uses: CXX and MPI.

openPMDConfig.cmake.in

@@ -31,7 +31,12 @@ set(openPMD_HDF5_FOUND ${openPMD_HAVE_HDF5})
 
 set(openPMD_HAVE_ADIOS2 @openPMD_HAVE_ADIOS2@)
 if(openPMD_HAVE_ADIOS2)
-    find_dependency(ADIOS2)
+    set(openPMD_REQUIRED_ADIOS2_COMPONENTS CXX)
+    if(openPMD_HAVE_MPI)
+        LIST(APPEND openPMD_REQUIRED_ADIOS2_COMPONENTS MPI)
+    endif()
+    find_dependency(ADIOS2 COMPONENTS ${openPMD_REQUIRED_ADIOS2_COMPONENTS})
+    unset(openPMD_REQUIRED_ADIOS2_COMPONENTS)
 endif()
 set(openPMD_ADIOS2_FOUND ${openPMD_HAVE_ADIOS2})