Tegra: include platform_def.h to access UART macros

This patch includes platform_def.h required to access UART macros -
"TEGRA_BOOT_UART_CLK_IN_HZ" and "TEGRA_CONSOLE_BAUDRATE" from
tegra_helpers.S.

Change-Id: Ieb63968a48dc299d03e81ddeb1ccc871cf3397a1
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>

plat/nvidia/tegra/common/aarch64/tegra_helpers.S

@@ -33,6 +33,7 @@
 #include <cpu_macros.S>
 #include <cortex_a57.h>
 #include <cortex_a53.h>
+#include <platform_def.h>
 #include <tegra_def.h>
 
 #define MIDR_PN_CORTEX_A57		0xD07