net: Add DM9051 driver

Add davicom dm9051 SPI ethernet driver. The driver work with some
parameters, such as:

 - spi bus number

 - spi chip select

 - spi clock frequency

 - interrupt gpio pin

Interrupt polarity fixed to low.
Test OK with Raspberry Pi 2 and Pi 4 as well for its broadcom CPUs.
This driver can work to many other CPUs too, since it independently
uses the lower spi control functions that are provided from the CPU
vendors.

Signed-off-by: Joseph CHANG <josright123@gmail.com>

drivers/net/ethernet/davicom/Kconfig

@@ -3,6 +3,20 @@
 # Davicom device configuration
 #
 
+config NET_VENDOR_DAVICOM
+	bool "Davicom devices"
+	depends on ARM || MIPS || COLDFIRE || NIOS2 || COMPILE_TEST || SPI
+	default y
+	help
+	  If you have a network (Ethernet) card belonging to this class, say Y.
+
+	  Note that the answer to this question doesn't directly affect the
+	  kernel: saying N will just cause the configurator to skip all
+	  the questions about Davicom devices. If you say Y, you will be asked
+	  for your specific card in the following selections.
+
+if NET_VENDOR_DAVICOM
+
 config DM9000
 	tristate "DM9000 support"
 	depends on ARM || MIPS || COLDFIRE || NIOS2 || COMPILE_TEST
@@ -22,3 +36,19 @@ config DM9000_FORCE_SIMPLE_PHY_POLL
 	  bit to determine if the link is up or down instead of the more
 	  costly MII PHY reads. Note, this will not work if the chip is
 	  operating with an external PHY.
+
+config DM9051
+	tristate "DM9051 SPI support"
+	depends on SPI
+	select CRC32
+	select MII
+	help
+	  Support for DM9051 SPI chipset.
+
+	  To compile this driver as a module, choose M here.  The module
+	  will be called dm9051.
+
+	  The SPI mode for the host's SPI master to access DM9051 is mode
+	  0 on the SPI bus.
+
+endif # NET_VENDOR_DAVICOM

drivers/net/ethernet/davicom/Makefile

@@ -4,3 +4,4 @@
 #
 
 obj-$(CONFIG_DM9000) += dm9000.o
+obj-$(CONFIG_DM9051) += dm9051.o