CMake: Fix dirs and sources visibility for mbed-emac CMake target

The mbed-emac CMake target is an interface library and as such its
include dirs and sources have to be have the INTERFACE visibility.

Author: harrisonmutai-arm

connectivity/drivers/emac/TARGET_RENESAS_EMAC/TARGET_RZ_A2XX/CMakelists.txt

@@ -2,17 +2,16 @@
 # SPDX-License-Identifier: Apache-2.0
 
 target_include_directories(mbed-emac
-    PUBLIC
+    INTERFACE
         .
         r_ether_rza2
         r_ether_rza2/src/phy
         r_ether_rza2/src/targets/TARGET_GR_MANGO
-    PRIVATE
         r_ether_rza2/src
 )
 
 target_sources(mbed-emac
-    PRIVATE
+    INTERFACE
         rza2_emac.cpp
         r_ether_rza2/src/r_ether_rza2.c
         r_ether_rza2/src/phy/phy.c