boards/seeedstudio-gd32: extend Kconfig by clock configuration

The configuration whether a HXTAL is present and what its clock frequency is will be added to Kconfig. Since it is the only GD32V board at the moment, the configuration is added to the Kconfig of the board, but should be moved to a common Kconfig later when more GD32V boards are added.

boards/seeedstudio-gd32/Kconfig

@@ -13,3 +13,19 @@ config BOARD_SEEEDSTUDIO_GD32
     default y
     select CPU_MODEL_GD32VF103VBT6
     select HAS_PERIPH_UART
+    select BOARD_HAS_HXTAL
+    select BOARD_HAS_LXTAL
+
+config BOARD_HAS_HXTAL
+    bool
+    help
+        Indicates that the board is providing an HXTAL oscillator
+
+config BOARD_HAS_LXTAL
+    bool
+    help
+        Indicates that the board is providing an LXTAL oscillator
+
+config CLOCK_HXTAL
+    int
+    default 80000000

boards/seeedstudio-gd32/include/periph_conf.h

@@ -28,11 +28,14 @@ extern "C" {
 
 /* This board provides an high frequency oscillator */
 #ifndef CONFIG_BOARD_HAS_HXTAL
-#define CONFIG_BOARD_HAS_HXTAL        1
+#define CONFIG_BOARD_HAS_HXTAL  1
 #endif
 
-#define CLOCK_HXTAL         MHZ(8)             /**< HXTAL frequency */
-#define CLOCK_CORECLOCK     MHZ(108)           /**< CPU clock frequency in Hz */
+#ifndef CONFIG_CLOCK_HXTAL
+#define CONFIG_CLOCK_HXTAL      MHZ(8)      /**< HXTAL frequency */
+#endif
+
+#define CLOCK_CORECLOCK         MHZ(108)    /**< CPU clock frequency in Hz */
 
 /**
  * @name   Timer configuration

cpu/gd32v/clock.c

@@ -36,7 +36,7 @@
 #define PREDV0_CONF          1  /* Divide by 2 */
 #ifdef CONFIG_BOARD_HAS_HXTAL
 #define PLL_MULT_FACTOR      (CLOCK_CORECLOCK / \
-                                (CLOCK_HXTAL / (PREDV0_CONF + 1)) - 1)
+                                (CONFIG_CLOCK_HXTAL / (PREDV0_CONF + 1)) - 1)
 #else
 #define PLL_MULT_FACTOR      (CLOCK_CORECLOCK / (MHZ(8) / 2 ) - 1)
 #endif