sysreset: psci: use psci driver exported functions

Use psci driver exported functions for reset/poweroff, instead of
invoking directly invoke_psci_fn.

Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
diff --git a/drivers/sysreset/sysreset_psci.c b/drivers/sysreset/sysreset_psci.c
index c7907b3..83ecbcb 100644
--- a/drivers/sysreset/sysreset_psci.c
+++ b/drivers/sysreset/sysreset_psci.c
@@ -11,22 +11,18 @@
 
 static int psci_sysreset_request(struct udevice *dev, enum sysreset_t type)
 {
-	unsigned long function_id;
-
 	switch (type) {
 	case SYSRESET_WARM:
 	case SYSRESET_COLD:
-		function_id = PSCI_0_2_FN_SYSTEM_RESET;
+		psci_sys_reset(type);
 		break;
 	case SYSRESET_POWER_OFF:
-		function_id = PSCI_0_2_FN_SYSTEM_OFF;
+		psci_sys_poweroff();
 		break;
 	default:
 		return -ENOSYS;
 	}
 
-	invoke_psci_fn(function_id, 0, 0, 0);
-
 	return -EINPROGRESS;
 }