misc/printk: Make the default char_out routine weak

Architecture init code and/or HAL layers often have a working
"putchar" routine available long before the Zephyr driver layer is
initialized.

Make the default printk() output a weak symbol, so it can be
overridden on these platforms.

Also remove the kconfig depedency on CONSOLE_HAS_DRIVER, as this is a
non-driver mechanism.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>

misc/printk.c

@@ -40,9 +40,12 @@ static void _printk_hex_ulong(out_func_t out, void *ctx,
  * @brief Default character output routine that does nothing
  * @param c Character to swallow
  *
+ * Note this is defined as a weak symbol, allowing architecture code
+ * to override it where possible to enable very early logging.
+ *
  * @return 0
  */
-static int _nop_char_out(int c)
+ __attribute__((weak)) int z_arch_printk_char_out(int c)
 {
 	ARG_UNUSED(c);
 
@@ -50,7 +53,7 @@ static int _nop_char_out(int c)
 	return 0;
 }
 
-static int (*_char_out)(int) = _nop_char_out;
+int (*_char_out)(int) = z_arch_printk_char_out;
 
 /**
  * @brief Install the character output routine for printk

subsys/debug/Kconfig

@@ -104,7 +104,6 @@ config STACK_SENTINEL
 
 config PRINTK
 	bool "Send printk() to console"
-	depends on CONSOLE_HAS_DRIVER
 	default y
 	help
 	  This option directs printk() debugging output to the supported