drivers/dax: Allow to include DEV_DAX_PMEM as builtin

This move the dependency to DEV_DAX_PMEM_COMPAT such that only
if DEV_DAX_PMEM is built as module we can allow the compat support.

This allows to test the new code easily in a emulation setup where we
often build things without module support.

Cc: <stable@vger.kernel.org>
Fixes: 730926c3b0 ("device-dax: Add /sys/class/dax backwards compatibility")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dax/Kconfig

@@ -23,7 +23,6 @@ config DEV_DAX
 config DEV_DAX_PMEM
 	tristate "PMEM DAX: direct access to persistent memory"
 	depends on LIBNVDIMM && NVDIMM_DAX && DEV_DAX
-	depends on m # until we can kill DEV_DAX_PMEM_COMPAT
 	default DEV_DAX
 	help
 	  Support raw access to persistent memory.  Note that this
@@ -50,7 +49,7 @@ config DEV_DAX_KMEM
 
 config DEV_DAX_PMEM_COMPAT
 	tristate "PMEM DAX: support the deprecated /sys/class/dax interface"
-	depends on DEV_DAX_PMEM
+	depends on m && DEV_DAX_PMEM=m
 	default DEV_DAX_PMEM
 	help
 	  Older versions of the libdaxctl library expect to find all