split Makefile from Kbuild

This is needed because dkms sets KERNELRELEASE from command line.

Issue-id: #26
Signed-off-by: Jakub Kicinski <kubakici@wp.pl>

Kbuild

@@ -0,0 +1,10 @@
+EXTRA_CFLAGS += -Werror -Wenum-compare
+ccflags-y += -D__CHECK_ENDIAN__
+
+obj-m := mt7601u.o
+
+mt7601u-y := \
+	usb.o init.o main.o mcu.o trace.o dma.o core.o eeprom.o phy.o \
+	mac.o util.o debugfs.o tx.o
+
+CFLAGS_trace.o := -I$(src)

Makefile

@@ -1,21 +1,12 @@
-ifeq ($(KERNELRELEASE),)
+ifneq ($(KERNELRELEASE),)
+KDIR ?= /lib/modules/$(KERNELRELEASE)/build
+endif
+
 KDIR ?= /lib/modules/`uname -r`/build
+
 default:
 	$(MAKE) -C $(KDIR) M=$$PWD
 clean:
 	$(MAKE) -C $(KDIR) M=$$PWD clean
 install:
 	$(MAKE) -C $(KDIR) M=$$PWD modules_install
-else
-EXTRA_CFLAGS += -Werror -Wenum-compare
-ccflags-y += -D__CHECK_ENDIAN__
-
-obj-m := mt7601u.o
-
-mt7601u-y := \
-	usb.o init.o main.o mcu.o trace.o dma.o core.o eeprom.o phy.o \
-	mac.o util.o debugfs.o tx.o
-
-CFLAGS_trace.o := -I$(src)
-
-endif