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

lib/libc/printf.c

@@ -9,8 +9,6 @@
 #include <stdbool.h>
 #include <stdint.h>
 
-#include <common/debug.h>
-
 #define get_num_va_args(_args, _lcount)				\
 	(((_lcount) > 1)  ? va_arg(_args, long long int) :	\
 	(((_lcount) == 1) ? va_arg(_args, long int) :		\
@@ -43,6 +41,12 @@ static int unsigned_num_print(unsigned long long int unum, unsigned int radix,
 	int i = 0, count = 0;
 	unsigned int rem;
 
+	/* num_buf is only large enough for radix >= 10 */
+	if (radix < 10) {
+		assert(0);
+		return 0;
+	}
+
 	do {
 		rem = unum % radix;
 		if (rem < 0xa)