tests/drivers/adc: Switch to native_sim

Switch from native_posix to native_sim as default test platform.
For test with overlays, switch overlays and platform_allow from
native_posix to native_sim.
For tests without overlays, enable also in native_sim, and
set native_sim as integration platform.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

tests/drivers/adc/adc_emul/testcase.yaml

@@ -6,4 +6,8 @@ common:
 tests:
   drivers.adc.emul:
     depends_on: adc
-    platform_allow: native_posix
+    platform_allow:
+      - native_posix
+      - native_sim
+    integration_platforms:
+      - native_sim

tests/drivers/adc/adc_rescale/boards/native_sim_64.overlay

@@ -3,4 +3,4 @@
  *
  * SPDX-License-Identifier: Apache-2.0
  */
-#include "native_posix.overlay"
+#include "native_sim.overlay"

tests/drivers/adc/adc_rescale/testcase.yaml

@@ -3,4 +3,6 @@ common:
 tests:
   drivers.adc.rescale:
     depends_on: adc
-    platform_allow: native_posix
+    platform_allow:
+      - native_sim
+      - native_sim_64