thermal: rockchip: enhance the tsadc's bandgap feature for rk3399

Due to the voltage ripple, the sensing data of the tsadc is not accurate.
And in this patch, the bandgap feature is enhanced to remove the voltage
ripple, and then the tsadc can sense the temperature more precisely.

Obsolete codes are removed as well.

Signed-off-by: Rocky Hao <[e-mail]>
Signed-off-by: Caesar Wang <[e-mail]>
Cc: Eduardo Valentin <[e-mail]>
Cc: Zhang Rui <[e-mail]>
Cc: Heiko Stuebner <[e-mail]>
Cc: [e-mail]
Tested-by: Stephen Barber <[e-mail]>
Signed-off-by: Zhang Rui <[e-mail]>

drivers/thermal/rockchip_thermal.c

···
 #define GRF_TSADC_TESTBIT_L			0x0e648
 #define GRF_TSADC_TESTBIT_H			0x0e64c
 
-#define GRF_TSADC_TSEN_PD_ON			(0x30003 << 0)
-#define GRF_TSADC_TSEN_PD_OFF			(0x30000 << 0)
 #define GRF_SARADC_TESTBIT_ON			(0x10001 << 2)
 #define GRF_TSADC_TESTBIT_H_ON			(0x10001 << 2)
+#define GRF_TSADC_VCM_EN_L			(0x10001 << 7)
+#define GRF_TSADC_VCM_EN_H			(0x10001 << 7)
 
 /**
  * struct tsadc_table - code to temperature conversion table
···
 			       regs + TSADCV2_HIGHT_TSHUT_DEBOUNCE);
 
 	} else {
-		regmap_write(grf, GRF_TSADC_TESTBIT_L, GRF_TSADC_TSEN_PD_ON);
-		mdelay(10);
-		regmap_write(grf, GRF_TSADC_TESTBIT_L, GRF_TSADC_TSEN_PD_OFF);
+		/* Enable the voltage common mode feature */
+		regmap_write(grf, GRF_TSADC_TESTBIT_L, GRF_TSADC_VCM_EN_L);
+		regmap_write(grf, GRF_TSADC_TESTBIT_H, GRF_TSADC_VCM_EN_H);
+
 		usleep_range(15, 100); /* The spec note says at least 15 us */
 		regmap_write(grf, GRF_SARADC_TESTBIT, GRF_SARADC_TESTBIT_ON);
 		regmap_write(grf, GRF_TSADC_TESTBIT_H, GRF_TSADC_TESTBIT_H_ON);