Replace MediaTek delay timer by generic one

Use the generic delay timer instead of having a specific platform
file for configuring it.

Change-Id: If6b8f60bc04230f4b85b2bcc1b670fc65461214e
diff --git a/plat/mediatek/mt8173/platform.mk b/plat/mediatek/mt8173/platform.mk
index 1c550f3..8f48230 100644
--- a/plat/mediatek/mt8173/platform.mk
+++ b/plat/mediatek/mt8173/platform.mk
@@ -52,6 +52,7 @@
 				drivers/arm/gic/gic_v3.c			\
 				drivers/console/console.S			\
 				drivers/delay_timer/delay_timer.c		\
+				drivers/delay_timer/generic_delay_timer.c	\
 				lib/cpus/aarch64/aem_generic.S			\
 				lib/cpus/aarch64/cortex_a53.S			\
 				lib/cpus/aarch64/cortex_a57.S			\
@@ -72,7 +73,6 @@
 				${MTK_PLAT_SOC}/drivers/spm/spm_suspend.c	\
 				${MTK_PLAT_SOC}/drivers/timer/mt_cpuxgpt.c	\
 				${MTK_PLAT_SOC}/drivers/uart/8250_console.S	\
-				${MTK_PLAT_SOC}/plat_delay_timer.c		\
 				${MTK_PLAT_SOC}/plat_mt_gic.c			\
 				${MTK_PLAT_SOC}/plat_pm.c			\
 				${MTK_PLAT_SOC}/plat_sip_calls.c		\