soc/amd/picasso: use SMBus speed in compilation unit

The fixed bus speed of 400 kHz doesn't need to reside in a header file.
Just move the assumption into the code itself.

Change-Id: I8bb68607070d0daeae2ad3bcd79f49d5c20048fd
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38613
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/soc/amd/picasso/include/soc/smbus.h

@@ -19,8 +19,6 @@
 #include <stdint.h>
 #include <soc/iomap.h>
 
-#define SMB_SPEED_400KHZ		(66000000 / (400000 * 4))
-
 /*
  * Between 1-10 seconds, We should never timeout normally
  * Longer than this is just painful when a timeout condition occurs.

src/soc/amd/picasso/southbridge.c

@@ -253,8 +253,11 @@ void sb_read_mode(u32 mode)
 
 static void fch_smbus_init(void)
 {
+	/* 400 kHz smbus speed. */
+	const uint8_t smbus_speed = (66000000 / (400000 * 4));
+
 	pm_write8(SMB_ASF_IO_BASE, SMB_BASE_ADDR >> 8);
-	smbus_write8(SMBTIMING, SMB_SPEED_400KHZ);
+	smbus_write8(SMBTIMING, smbus_speed);
 	/* Clear all SMBUS status bits */
 	smbus_write8(SMBHSTSTAT, SMBHST_STAT_CLEAR);
 	smbus_write8(SMBSLVSTAT, SMBSLV_STAT_CLEAR);