fsl_i2c: Add CONFIG_FSL_I2C_CUSTOM_{DFSR/FDR}

Some boards need a higher DFSR value than the spec currently
recommends so give these boards the means to define there own.

For completeness, add CONFIG_FSL_I2C_CUSTOM_FDR too.
Signed-off-by: NJoakim Tjernlund <Joakim.Tjernlund@transmode.se>

drivers/i2c/fsl_i2c.c

@@ -172,14 +172,22 @@ static unsigned int set_i2c_bus_speed(const struct fsl_i2c *dev,
 			u8 fdr;
 #ifdef __PPC__
 			u8 dfsr;
+#ifdef CONFIG_FSL_I2C_CUSTOM_DFSR
+			dfsr = CONFIG_FSL_I2C_CUSTOM_DFSR;
+#else
 			dfsr = fsl_i2c_speed_map[i].dfsr;
 #endif
+			writeb(dfsr, &dev->dfsrr);	/* set default filter */
+#endif
+#ifdef CONFIG_FSL_I2C_CUSTOM_FDR
+			fdr = CONFIG_FSL_I2C_CUSTOM_FDR;
+			speed = i2c_clk / divider; /* Fake something */
+#else
 			fdr = fsl_i2c_speed_map[i].fdr;
 			speed = i2c_clk / fsl_i2c_speed_map[i].divider;
-			writeb(fdr, &dev->fdr);		/* set bus speed */
-#ifdef __PPC__
-			writeb(dfsr, &dev->dfsrr);	/* set default filter */
 #endif
+			writeb(fdr, &dev->fdr);		/* set bus speed */
+
 			break;
 		}