imx8: Replace PLAT_IMX8* with automatic PLAT_imx8*

Platform defines are already provided by the build system so let's not
duplicate them.

Change-Id: Icf1ea76c3c3213e27b447c95e2b22b961fa7693e
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
diff --git a/plat/imx/common/imx_sip_svc.c b/plat/imx/common/imx_sip_svc.c
index 45d18ef..4893b9f 100644
--- a/plat/imx/common/imx_sip_svc.c
+++ b/plat/imx/common/imx_sip_svc.c
@@ -31,7 +31,7 @@
 		SMC_RET1(handle, imx_soc_info_handler(smc_fid, x1, x2, x3));
 		break;
 #endif
-#if (defined(PLAT_IMX8QM) || defined(PLAT_IMX8QX))
+#if (defined(PLAT_imx8qm) || defined(PLAT_imx8qx))
 	case  IMX_SIP_SRTC:
 		return imx_srtc_handler(smc_fid, handle, x1, x2, x3, x4);
 	case  IMX_SIP_CPUFREQ: