imx: enable IRQ steer wakeup source support

Enable IRQ steer wakeup source support for Linux kernel
wakeup sources like debug UART wakeup etc..

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
diff --git a/plat/imx/common/imx8_sip_svc.c b/plat/imx/common/imx8_sip_svc.c
index a47f85a..3929dd4 100644
--- a/plat/imx/common/imx8_sip_svc.c
+++ b/plat/imx/common/imx8_sip_svc.c
@@ -60,6 +60,9 @@
 		break;
 	case  IMX_SIP_SRTC:
 		return imx_srtc_handler(smc_fid, handle, x1, x2, x3, x4);
+	case  IMX_SIP_WAKEUP_SRC:
+		SMC_RET1(handle, imx_wakeup_src_handler(smc_fid, x1, x2, x3));
+		break;
         case IMX_SIP_OTP_READ:
         case IMX_SIP_OTP_WRITE:
                 return imx_otp_handler(smc_fid, handle, x1, x2);