imx: add cpu-freq SIP runtime service support

On i.MX8QM/i.MX8QX with system controller inside, the CPU's clock
rate is managed by SCFW(system controller firmware) and can ONLY be
changed from secure world, so SIP runtime service is needed for
setting CPU's clock rate, this patch adds cpu-freq SIP runtime service
support.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
diff --git a/plat/imx/common/include/imx_sip_svc.h b/plat/imx/common/include/imx_sip_svc.h
index 0d21f75..4ba7b87 100644
--- a/plat/imx/common/include/imx_sip_svc.h
+++ b/plat/imx/common/include/imx_sip_svc.h
@@ -8,10 +8,15 @@
 #define __IMX_SIP_SVC_H__
 
 /* SMC function IDs for SiP Service queries */
+#define IMX_SIP_CPUFREQ			0xC2000001
+#define IMX_SIP_SET_CPUFREQ		0x00
+
 #define IMX_SIP_SRTC			0xC2000002
 #define IMX_SIP_SRTC_SET_TIME		0x00
 
 #if (defined(PLAT_IMX8QM) || defined(PLAT_IMX8QX))
+int imx_cpufreq_handler(uint32_t smc_fid, u_register_t x1,
+			u_register_t x2, u_register_t x3);
 int imx_srtc_handler(uint32_t smc_fid, void *handle, u_register_t x1,
 		     u_register_t x2, u_register_t x3, u_register_t x4);
 #endif