net: mhi: Add dedicated folder

Create a dedicated mhi directory for mhi-net, mhi-net is going to
be split into differente files (for additional protocol support).

Signed-off-by: Loic Poulain <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/Makefile

···
 obj-$(CONFIG_NLMON) += nlmon.o
 obj-$(CONFIG_NET_VRF) += vrf.o
 obj-$(CONFIG_VSOCKMON) += vsockmon.o
-obj-$(CONFIG_MHI_NET) += mhi_net.o
+obj-$(CONFIG_MHI_NET) += mhi/
 
 #
 # Networking Drivers

drivers/net/mhi/Makefile

···
+obj-$(CONFIG_MHI_NET) += mhi_net.o
+
+mhi_net-y := net.o