genet: add module (if_genet.ko)

The driver already had the appropriate module macros, it just wasn't
hooked into the build system.

Since this device is specific to the Raspberry Pi 4, only build it for
AArch64.

Reviewed by: imp, emaste (earlier version)
Pull Request: https://github.com/freebsd/freebsd-src/pull/1139

sys/modules/Makefile

@@ -154,6 +154,7 @@ SUBDIR=	\
 	if_edsc \
 	${_if_enc} \
 	if_epair \
+	${_genet} \
 	${_if_gif} \
 	${_if_gre} \
 	${_if_me} \
@@ -641,6 +642,11 @@ _cxgbe=		cxgbe
 _mpi3mr=mpi3mr
 .endif
 
+# Specific to the Raspberry Pi.
+.if ${MACHINE_CPUARCH} == "aarch64"
+_genet=		genet
+.endif
+
 .if ${MACHINE_CPUARCH} == "amd64" || ${MACHINE_CPUARCH} == "aarch64" || \
 	${MACHINE_ARCH:Mpowerpc64*}
 _ice=		ice

sys/modules/genet/Makefile

@@ -0,0 +1,9 @@
+
+.PATH: ${SRCTOP}/sys/arm64/broadcom/genet
+
+KMOD=	if_genet
+SRCS=	if_genet.c
+SRCS+=	bus_if.h device_if.h gpio_if.h miibus_if.h ofw_bus_if.h syscon_if.h
+SRCS+=	opt_device_polling.h opt_platform.h
+
+.include <bsd.kmod.mk>