ipc/cmake: use the new add_local_sources() indirection layer

In the review of commit 1bd9e0d ("cmake/zephyr: decentralize
src/ipc/"), Andy recommended "maybe work around this by adding yet
another layer of indirection". I rejected the idea at the time because
the level of duplication in the ipc/ directory was small. Then I looked
at the bigger math/ subdirectory and I realized in #8548 that such an
indirection layer is actually required for bigger and/or more complex
cases. So I added that layer of indirection in commit
330d73e ("cmake: a few new add_local_sources[_ifdef]()
compatibility macros")

Now that we have it, we might as well use it and perform small
simplifications in ipc/cmake.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

src/ipc/CMakeLists.txt

@@ -6,7 +6,8 @@ elseif (CONFIG_IPC_MAJOR_4)
         add_subdirectory(ipc4)
 endif()
 
-set(base_files
+# Common to Zephyr and XTOS
+add_local_sources(sof
 	ipc-common.c
 	ipc-helper.c
 )
@@ -15,7 +16,6 @@ is_zephyr(it_is)
 if(it_is) ###  Zephyr ###
 
 zephyr_library_sources(
-	${base_files}
 	dma-copy.c
 )
 
@@ -29,10 +29,6 @@ endif()
 else() ###  Not Zephyr ###
 
 
-add_local_sources(sof
-	${base_files}
-)
-
 if (CONFIG_TRACE)
 	add_local_sources(sof
 		dma-copy.c)

src/ipc/ipc3/CMakeLists.txt

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 
-set(common_files
+# Files common to Zephyr and XTOS
+add_local_sources(sof
 		handler.c
 		helper.c
 		dai.c
@@ -10,16 +11,11 @@ is_zephyr(it_is)
 if(it_is) ###  Zephyr ###
 
 zephyr_library_sources(
-	${common_files}
 	host-page-table.c
 )
 
 else()  ### Not Zephyr ###
 
-add_local_sources(sof
-	${common_files}
-)
-
 if (CONFIG_HOST_PTABLE)
 	add_local_sources(sof
 		host-page-table.c)

src/ipc/ipc4/CMakeLists.txt

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 
-set(common_files
+# Files common to Zephyr and XTOS
+add_local_sources(sof
 	dai.c
 	handler.c
 	helper.c
@@ -12,11 +13,6 @@ set(common_files
 is_zephyr(it_is)
 if(it_is) ###  Zephyr ###
 
-
-zephyr_library_sources(
-	${common_files}
-)
-
 zephyr_library_sources_ifdef(CONFIG_AMS
 	ams_helpers.c
 )
@@ -26,7 +22,6 @@ else()  ### Not Zephyr ####
 
 
 add_local_sources(sof
-	${common_files}
 	ams_helpers.c
 )