Allow using this tree with dkms

* Add dkms.conf
* Make Makefile dkms-friendly

Makefile

@@ -3,11 +3,13 @@
 # Makefile for the out-of-tree Linux APFS module.
 #
 
+KERNELRELEASE ?= $(shell uname -r)
+
 obj-m = apfs.o
 apfs-y = btree.o dir.o extents.o file.o inode.o key.o message.o \
 	 namei.o node.o object.o super.o symlink.o unicode.o xattr.o
 
 default:
-	make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd)
+	make -C /lib/modules/$(KERNELRELEASE)/build M=$(shell pwd)
 clean:
-	make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) clean
+	make -C /lib/modules/$(KERNELRELEASE)/build M=$(shell pwd) clean

dkms.conf

@@ -0,0 +1,7 @@
+PACKAGE_NAME="linux-apfs"
+PACKAGE_VERSION="0.1"
+
+BUILT_MODULE_NAME[0]="apfs"
+DEST_MODULE_LOCATION[0]="/extra"
+
+AUTOINSTALL="yes"