mediatek: move uart.h to common folder

UART register definition is the same on MediaTek platforms.
Move uart.h to common folder and remove the duplicate file.

Change-Id: Iea0931dfd606ae4a7ab475b9cb3a08dc6de68b36
diff --git a/plat/mediatek/mt8192/platform.mk b/plat/mediatek/mt8192/platform.mk
index 0b35d06..e45f649 100644
--- a/plat/mediatek/mt8192/platform.mk
+++ b/plat/mediatek/mt8192/platform.mk
@@ -8,6 +8,7 @@
 MTK_PLAT_SOC  := ${MTK_PLAT}/${PLAT}
 
 PLAT_INCLUDES := -I${MTK_PLAT}/common/                            \
+                 -I${MTK_PLAT}/common/drivers/uart/                \
                  -I${MTK_PLAT}/common/lpm/                        \
                  -I${MTK_PLAT_SOC}/include/                       \
                  -I${MTK_PLAT_SOC}/drivers/                       \
@@ -19,8 +20,7 @@
                  -I${MTK_PLAT_SOC}/drivers/ptp3/                  \
                  -I${MTK_PLAT_SOC}/drivers/rtc/                   \
                  -I${MTK_PLAT_SOC}/drivers/spmc/                  \
-                 -I${MTK_PLAT_SOC}/drivers/timer/                 \
-                 -I${MTK_PLAT_SOC}/drivers/uart/
+                 -I${MTK_PLAT_SOC}/drivers/timer/
 
 GICV3_SUPPORT_GIC600        :=      1
 include drivers/arm/gic/v3/gicv3.mk