ARM: dts: imx6sx-sdb: Add 198MHz operational point

imx6sx-sdb has custom operating points entries because it has one
power supply that drives both VDDARM_IN and VDDSOC_IN.

As per the MX6UL datasheet we have the following minimum voltages for
198 MHz operation (after adding the 25mV margin value):
VDDARM_IN = 0.975 V
VDDSOC_IN = 1.175 V

So use 1.175V for the 198MHz operation.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6sx-sdb.dts

@@ -18,12 +18,14 @@ &cpu0 {
 		996000  1250000
 		792000  1175000
 		396000  1175000
+		198000  1175000
 		>;
 	fsl,soc-operating-points = <
 		/* ARM kHz      SOC uV */
 		996000	1250000
 		792000	1175000
 		396000	1175000
+		198000  1175000
 	>;
 };