refactor(libc): clean up dependencies in libc

- Removing platform dependencies from libc modules.
- Replacing panicking with actual error handling.
- Debug macros are included indirectly from assert.h. Removing
  "platform_def.h" from assert.h and adding "common/debug.h"
  where the macros are used.
- Removing hack for fixing PLAT_LOG_LEVEL_ASSERT to 40.
  Instead removing assert with expression, as this
  does not provide additional information.

Signed-off-by: Claus Pedersen <claustbp@google.com>
Change-Id: Icc201ea7b63c1277e423c1cfd13fd6816c2bc568
diff --git a/plat/xilinx/common/include/plat_startup.h b/plat/xilinx/common/include/plat_startup.h
index 5ccb774..1733930 100644
--- a/plat/xilinx/common/include/plat_startup.h
+++ b/plat/xilinx/common/include/plat_startup.h
@@ -7,6 +7,8 @@
 #ifndef PLAT_STARTUP_H
 #define PLAT_STARTUP_H
 
+#include <common/bl_common.h>
+
 /* For FSBL handover */
 enum fsbl_handoff {
 	FSBL_HANDOFF_SUCCESS = 0,