[stm32f4] add I2C frequencies

STM32F4 allows I2C frequencies up to 42 MHz, this commit adds the missing
defines.

include/libopencm3/stm32/common/i2c_common_all.h

@@ -165,7 +165,8 @@ specific memorymap.h header before including this header file.*/
 
 /* Note: Bits [7:6] are reserved, and forced to 0 by hardware. */
 
-/* FREQ[5:0]: Peripheral clock frequency (valid values: 2-36 MHz) */
+/* FREQ[5:0]: Peripheral clock frequency (valid values: 2-36 MHz, 2-42 MHz for
+ * STM32F4 respectivly) */
 /****************************************************************************/
 /** @defgroup i2c_clock I2C clock frequency settings
 @ingroup i2c_defines
@@ -206,6 +207,12 @@ specific memorymap.h header before including this header file.*/
 #define I2C_CR2_FREQ_34MHZ		0x22
 #define I2C_CR2_FREQ_35MHZ		0x23
 #define I2C_CR2_FREQ_36MHZ		0x24
+#define I2C_CR2_FREQ_37MHZ		0x25
+#define I2C_CR2_FREQ_38MHZ		0x26
+#define I2C_CR2_FREQ_39MHZ		0x27
+#define I2C_CR2_FREQ_40MHZ		0x28
+#define I2C_CR2_FREQ_41MHZ		0x29
+#define I2C_CR2_FREQ_42MHZ		0x2a
 /**@}*/
 
 /* --- I2Cx_OAR1 values ---------------------------------------------------- */