mvebu: Turris Omnia: use SFP module, if present

Follow the recommendations stated in the Turris Omnia DTS for eth2:

"In case SFP module is present, U-Boot has to enable the sfp node above,
remove phy-handle property, and add managed = "in-band-status" property."

The boot script is written in a way, that it works for all U-Boot
versions deployed by the vendor so far (2015.10-rc2, 2019.07).

Reviewed-by: Noci <noci@noci.work>
Reviewed-by: Justin van Steijn <jvs@fsfe.org>
Reviewed-by: Nico Rikken <nico@nicorikken.eu>
Reviewed-by: Julius Schwartzenberg <julius.schwartzenberg@gmail.com>
Signed-off-by: Klaus Kudielka <klaus.kudielka@gmail.com>
(cherry picked from commit 23d2690e5a5410576b587bc96e2c2cf5fc693927)

target/linux/mvebu/image/turris-omnia.bootscript

@@ -11,7 +11,22 @@ else
 fi
 setenv bootargs earlyprintk console=ttyS0,115200 root=${rootdev} rootfstype=auto rootwait
 
-# Load and boot
+# Load device tree and prepare for modification
 load ${devtype} ${devnum}:${distro_bootpart} ${fdt_addr_r} @DTB@.dtb
+fdt addr ${fdt_addr_r}
+fdt resize
+
+# Enable SFP cage, if module is present
+i2c dev 0
+i2c mw 0x70 0.0 0xf
+i2c read 0x71 0 1 0x00fffff1
+setexpr.b mod_def0 *0x00fffff1 \& 0x10
+if test ${mod_def0} -eq 0; then
+	fdt set /sfp status okay
+	fdt rm /soc/internal-regs/ethernet@34000 phy-handle
+	fdt set /soc/internal-regs/ethernet@34000 managed in-band-status
+fi
+
+# Load kernel and boot
 load ${devtype} ${devnum}:${distro_bootpart} ${kernel_addr_r} zImage
 bootz ${kernel_addr_r} - ${fdt_addr_r}