xilinx: Move zynq_board_read_rom_ethaddr to shared location

Zynq and ZynqMP are sharing similar code and there is no reason to do
code duplication. Move zynq_board_read_rom_ethaddr() to common file for
easier conversion to DM.
Use ZynqMP version that's why also add CONFIG_ZYNQ_EEPROM_BUS to Syzygy
which is only one Zynq board which is using this feature.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/include/configs/syzygy_hub.h b/include/configs/syzygy_hub.h
index 88ee772..7503697 100644
--- a/include/configs/syzygy_hub.h
+++ b/include/configs/syzygy_hub.h
@@ -12,6 +12,7 @@
 
 #define CONFIG_SYS_I2C_EEPROM_ADDR_LEN 1
 #define CONFIG_ZYNQ_GEM_EEPROM_ADDR    0x57
+#define CONFIG_ZYNQ_EEPROM_BUS		0
 
 #define CONFIG_EXTRA_ENV_SETTINGS       \
 	"fit_image=fit.itb\0"		\