More Makefile Fixes

The Makefile wasn't in the appropriate format for DKMS. While it did
work on the Coral Dev Board, it failed on other devices.

Tested:
Coral Dev Board, x86 Debian Machine

src/Makefile

@@ -7,3 +7,11 @@ obj-m += apex.o
 
 gasket-objs	:= gasket_core.o gasket_ioctl.o gasket_interrupt.o gasket_page_table.o gasket_sysfs.o
 apex-objs	:= apex_driver.o
+
+KVERSION := $(shell uname -r)
+
+all:
+	$(MAKE) -C /lib/modules/$(KVERSION)/build M=$(PWD) modules
+
+clean:
+	$(MAKE) -C /lib/modules/$(KVERSION)/build M=$(PWD) clean