cxl: Move cxl_core to new directory

CXL core is growing, and it's already arguably unmanageable. To support
future growth, move core functionality to a new directory and rename the
file to represent just bus support. Future work will remove non-bus
functionality.

Note that mem.h is renamed to cxlmem.h to avoid a namespace collision
with the global ARCH=um mem.h header.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/162792537866.368511.8915631504621088321.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

Documentation/driver-api/cxl/memory-devices.rst

@@ -36,7 +36,7 @@ CXL Core
 .. kernel-doc:: drivers/cxl/cxl.h
    :internal:
 
-.. kernel-doc:: drivers/cxl/core.c
+.. kernel-doc:: drivers/cxl/core/bus.c
    :doc: cxl core
 
 External Interfaces

drivers/cxl/Makefile

 # SPDX-License-Identifier: GPL-2.0
-obj-$(CONFIG_CXL_BUS) += cxl_core.o
+obj-$(CONFIG_CXL_BUS) += core/
 obj-$(CONFIG_CXL_MEM) += cxl_pci.o
 obj-$(CONFIG_CXL_ACPI) += cxl_acpi.o
 obj-$(CONFIG_CXL_PMEM) += cxl_pmem.o
 
-ccflags-y += -DDEFAULT_SYMBOL_NAMESPACE=CXL
-cxl_core-y := core.o
 cxl_pci-y := pci.o
 cxl_acpi-y := acpi.o
 cxl_pmem-y := pmem.o

drivers/cxl/core/Makefile

+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_CXL_BUS) += cxl_core.o
+
+ccflags-y += -DDEFAULT_SYMBOL_NAMESPACE=CXL -I$(srctree)/drivers/cxl
+cxl_core-y := bus.o

drivers/cxl/core.c → drivers/cxl/core/bus.c

@@ -6,8 +6,8 @@
 #include <linux/pci.h>
 #include <linux/slab.h>
 #include <linux/idr.h>
-#include "cxl.h"
-#include "mem.h"
+#include <cxlmem.h>
+#include <cxl.h>
 
 /**
  * DOC: cxl core

drivers/cxl/pci.c

@@ -12,9 +12,9 @@
 #include <linux/pci.h>
 #include <linux/io.h>
 #include <linux/io-64-nonatomic-lo-hi.h>
+#include "cxlmem.h"
 #include "pci.h"
 #include "cxl.h"
-#include "mem.h"
 
 /**
  * DOC: cxl pci

drivers/cxl/pmem.c

@@ -6,7 +6,7 @@
 #include <linux/ndctl.h>
 #include <linux/async.h>
 #include <linux/slab.h>
-#include "mem.h"
+#include "cxlmem.h"
 #include "cxl.h"
 
 /*