net: gem: Add driver dependencies to PHYLIB

Clear driver dependecies via Kconfig. Remove PHYLIB dependency from
the driver.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index e77797a..ae5e78d 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -103,6 +103,7 @@
 
 config ZYNQ_GEM
 	depends on DM_ETH && (ARCH_ZYNQ || ARCH_ZYNQMP)
+	select PHYLIB
 	bool "Xilinx Ethernet GEM"
 	help
 	  This MAC is present in Xilinx Zynq and ZynqMP SoCs.