tools/testing/cxl: Prevent cxl_test from confusing production modules

The cxl_test machinery builds modified versions of the modules in
drivers/cxl/ and intercepts some of their calls to allow cxl_test to
inject mock CXL topologies for test.

However, if cxl_test attempts the same with production modules,
fireworks ensue as Luis discovered [1]. Prevent that scenario by
arranging for cxl_test to check for a "watermark" symbol in each of the
modules it expects to be modified before the test can run. This turns
undefined runtime behavior or crashes into a safer failure to load the
cxl_test module.

Link: http://lore.kernel.org/r/20221209062919.1096779-1-mcgrof@kernel.org [1]
Reported-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

tools/testing/cxl/Kbuild

@@ -24,22 +24,27 @@ obj-m += cxl_acpi.o
 cxl_acpi-y := $(CXL_SRC)/acpi.o
 cxl_acpi-y += mock_acpi.o
 cxl_acpi-y += config_check.o
+cxl_acpi-y += cxl_acpi_test.o
 
 obj-m += cxl_pmem.o
 
 cxl_pmem-y := $(CXL_SRC)/pmem.o
 cxl_pmem-y += $(CXL_SRC)/security.o
 cxl_pmem-y += config_check.o
+cxl_pmem-y += cxl_pmem_test.o
 
 obj-m += cxl_port.o
 
 cxl_port-y := $(CXL_SRC)/port.o
 cxl_port-y += config_check.o
+cxl_port-y += cxl_port_test.o
+
 
 obj-m += cxl_mem.o
 
 cxl_mem-y := $(CXL_SRC)/mem.o
 cxl_mem-y += config_check.o
+cxl_mem-y += cxl_mem_test.o
 
 obj-m += cxl_core.o
 
@@ -53,5 +58,6 @@ cxl_core-y += $(CXL_CORE_SRC)/hdm.o
 cxl_core-$(CONFIG_TRACING) += $(CXL_CORE_SRC)/trace.o
 cxl_core-$(CONFIG_CXL_REGION) += $(CXL_CORE_SRC)/region.o
 cxl_core-y += config_check.o
+cxl_core-y += cxl_core_test.o
 
 obj-m += test/