Split PHY code into phy.{c,h}; add PHY config to STM32H driver

src/drivers/phy.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include "net_builtin.h"
+
+struct mg_phy {
+  uint16_t (*read_reg)(uint8_t addr, uint8_t reg);
+  void (*write_reg)(uint8_t addr, uint8_t reg, uint16_t value);
+};
+
+// PHY configuration settings, bitmask
+enum {
+  MG_PHY_LEDS_ACTIVE_HIGH =
+      (1 << 0),  // Set if PHY LEDs are connected to ground
+  MG_PHY_CLOCKS_MAC =
+      (1 << 1),  // Set when PHY clocks MAC. Otherwise, MAC clocks PHY
+};
+
+enum { MG_PHY_SPEED_10M, MG_PHY_SPEED_100M, MG_PHY_SPEED_1000M };
+
+void mg_phy_init(struct mg_phy *, uint8_t addr, uint8_t config);
+bool mg_phy_up(struct mg_phy *, uint8_t addr, bool *full_duplex,
+               uint8_t *speed);