cmake: link programs that only use crypto with libmbedcrypto

When building with CMake, for sample programs that only use
functionality in libmbedcrypto (i.e. crypto and platform), link with
libmbedcrypto, not with libmbedtls.

This doesn't change the result, because the linker skips libraries in
which no symbol is used, but it changes the build dependencies, and it
has the advantage of bringing programs/*/CMakeLists.txt closer to the
corresponding files under crypto/.

The programs concerned are crypto sample and test programs, and
programs that only use (potential) platform functions such as
mbedtls_printf. dh_client and dh_server keep linking with mbedtls
because they use functions from the net_sockets module.
diff --git a/programs/aes/CMakeLists.txt b/programs/aes/CMakeLists.txt
index f5a0caa..6c4c7e1 100644
--- a/programs/aes/CMakeLists.txt
+++ b/programs/aes/CMakeLists.txt
@@ -1,8 +1,8 @@
 add_executable(aescrypt2 aescrypt2.c)
-target_link_libraries(aescrypt2 mbedtls)
+target_link_libraries(aescrypt2 mbedcrypto)
 
 add_executable(crypt_and_hash crypt_and_hash.c)
-target_link_libraries(crypt_and_hash mbedtls)
+target_link_libraries(crypt_and_hash mbedcrypto)
 
 install(TARGETS aescrypt2 crypt_and_hash
         DESTINATION "bin"