logging: Add LOG_PRINTK macro for printing via logging

Added macro which allows to print formatted string using
logging infrastructure.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>

include/logging/log.h

@@ -70,6 +70,17 @@ extern "C" {
  */
 #define LOG_DBG(...)    Z_LOG(LOG_LEVEL_DBG, __VA_ARGS__)
 
+/**
+ * @brief Unconditionally print raw log message.
+ *
+ * The result is same as if printk was used but it goes through logging
+ * infrastructure thus utilizes logging mode, e.g. deferred mode.
+ *
+ * @param ... A string optionally containing printk valid conversion specifier,
+ * followed by as many values as specifiers.
+ */
+#define LOG_PRINTK(...) Z_LOG_PRINTK(__VA_ARGS__)
+
 /**
  * @brief Writes an ERROR level message associated with the instance to the log.
  *