Update degree symbol to utf-8 encoding in comments

Almost all of the places where we have the degree symbol '°', it's
encoded as 0xc2 0xb0 (utf-8 encoding).  There are a few places where it
is encoded as just a high ascii byte: 0xb0.  Editors that support the
high ascii 0xb0 seem to support the utf-8 0xc2 0xb0 encoding as well,
but the opposite does not seem to be true.

Change the high-ascii degree symbols to utf-8 encoding.

Change-Id: I3d06289b802f45e938dc72b4c437fca56235b62b
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/15978
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Alexander Couzens <lynxis@fe80.eu>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/mainboard/ibase/mb899/cmos.layout

@@ -142,7 +142,7 @@ enumerations
 9    14     1527
 9    15     1406
 #
-# Temperature (°C/°F)
+# Temperature (°C/°F)
 #10     0     30/86
 #10     1     33/91
 #10     2     36/96

src/mainboard/siemens/sitemp_g1p1/cmos.layout

@@ -132,7 +132,7 @@ enumerations
 # CPU/Chassis FAN Control: polarity
 13  0   Active_high
 13  1   Active_low
-# Temperature °C
+# Temperature °C
 14  0   30
 14  1   35
 14  2   40

src/mainboard/siemens/sitemp_g1p1/mainboard.c

@@ -362,16 +362,16 @@ static const char * adt7475_detect( void ) {
 const struct fan_control cpu_fan_control_defaults = {
 	.enable = 0, // disable by default
 	.polarity = 0, // high by default
-	.t_min = 3, // default = 45°C
-	.t_max = 7, // 65°C
+	.t_min = 3, // default = 45°C
+	.t_max = 7, // 65°C
 	.pwm_min = 1, // default dutycycle = 30%
 	.pwm_max = 13, // 90%
 };
 const struct fan_control case_fan_control_defaults = {
 	.enable = 0, // disable by default
 	.polarity = 0, // high by default
-	.t_min = 2, // default = 40°C
-	.t_max = 8, // 70°C
+	.t_min = 2, // default = 40°C
+	.t_max = 8, // 70°C
 	.pwm_min = 0, // default dutycycle = 25%
 	.pwm_max = 13, // 90%
 };