rockchip: on rk3399 enable Schmitt trigger on 32 kHz clock

If we don't enable the Schmitt trigger on the 32 kHz clock then systems
won't always resume from suspend properly.  Presumably anything else in
the system that relies on the 32 kHz clock also will have problems
without the Schmitt trigger enabled.

Enable it always since having the 32 kHz clock on GPIO0_A0 isn't
exactly an optional feature, so all boards using rk3399 will need this.

Change-Id: Idc18c6cd1adc5be5f60efd9cb805d83d5cd40129

plat/rockchip/rk3399/drivers/pmu/pmu.c

@@ -1078,6 +1078,12 @@ void plat_rockchip_pmu_init(void)
 		      CPU_BOOT_ADDR_WMASK);
 	mmio_write_32(PMU_BASE + PMU_NOC_AUTO_ENA, NOC_AUTO_ENABLE);
 
+	/*
+	 * Enable Schmitt trigger for better 32 kHz input signal, which is
+	 * important for suspend/resume reliability among other things.
+	 */
+	mmio_write_32(PMUGRF_BASE + PMUGRF_GPIO0A_SMT, GPIO0A0_SMT_ENABLE);
+
 	init_pmu_counts();
 
 	nonboot_cpus_off();

plat/rockchip/rk3399/drivers/pmu/pmu.h

@@ -819,6 +819,7 @@ enum pmu_core_pwr_st {
 
 #define AP_PWROFF		0x0a
 
+#define GPIO0A0_SMT_ENABLE	BITS_WITH_WMASK(1, 3, 0)
 #define GPIO1A6_IOMUX		BITS_WITH_WMASK(0, 3, 12)
 
 #define TSADC_INT_PIN		38
@@ -876,6 +877,7 @@ enum pmu_core_pwr_st {
 #define	GRF_SOC_CON4		0x0e210
 #define GRF_GPIO4C_IOMUX	0x0e028
 
+#define PMUGRF_GPIO0A_SMT	0x0120
 #define PMUGRF_SOC_CON0		0x0180
 
 #define CCI_FORCE_WAKEUP	WMSK_BIT(8)