soc: fix compiling unit tests with CMake

soc unit tests have not been included when compiling with CMake,
because ../${SOC_NAME}/test was not evaluated relative to the
CMakeLists.txt directory.

Also call register_components() regardless of the presence of test
directory for particular target.

components/soc/test/CMakeLists.txt

@@ -1,9 +1,10 @@
 set(SOC_NAME ${IDF_TARGET})
-if(EXISTS "../${SOC_NAME}/test")
-    set(COMPONENT_SRCDIRS "../${SOC_NAME}/test")
-    set(COMPONENT_ADD_INCLUDEDIRS "../${SOC_NAME}/test")
-
-    set(COMPONENT_REQUIRES unity test_utils)
-
-    register_component()
+set(SOC_TEST_DIR ${CMAKE_CURRENT_SOURCE_DIR}/../${SOC_NAME}/test)
+if(EXISTS "${SOC_TEST_DIR}")
+    set(COMPONENT_SRCDIRS "${SOC_TEST_DIR}")
+    set(COMPONENT_ADD_INCLUDEDIRS "${SOC_TEST_DIR}")
 endif()
+
+set(COMPONENT_REQUIRES unity test_utils)
+
+register_component()