shell: add Kconfig option for configurable autoflush behavior

Introduced a new Kconfig option `SHELL_PRINTF_AUTOFLUSH` to allow
configuring the autoflush behavior of shell printing functions.

Updated `Z_SHELL_FPRINTF_DEFINE` to use the
`CONFIG_SHELL_PRINTF_AUTOFLUSH` setting instead of hardcoding
the autoflush behavior to `true`.

Signed-off-by: Jakub Rzeszutko <[email protected]>
(cherry picked from commit 8991b95)

Author: jakub-uC

include/zephyr/shell/shell.h

@@ -936,7 +936,8 @@ extern void z_shell_print_stream(const void *user_ctx, const char *data,
 	Z_SHELL_HISTORY_DEFINE(_name##_history, CONFIG_SHELL_HISTORY_BUFFER); \
 	Z_SHELL_FPRINTF_DEFINE(_name##_fprintf, &_name, _name##_out_buffer,   \
 			     CONFIG_SHELL_PRINTF_BUFF_SIZE,		      \
-			     true, z_shell_print_stream);		      \
+			     IS_ENABLED(CONFIG_SHELL_PRINTF_AUTOFLUSH),	      \
+			     z_shell_print_stream);			      \
 	LOG_INSTANCE_REGISTER(shell, _name, CONFIG_SHELL_LOG_LEVEL);	      \
 	Z_SHELL_STATS_DEFINE(_name);					      \
 	static K_KERNEL_STACK_DEFINE(_name##_stack, CONFIG_SHELL_STACK_SIZE); \

subsys/shell/Kconfig

@@ -89,6 +89,13 @@ config SHELL_PRINTF_BUFF_SIZE
 	  It is working like stdio buffering in Linux systems
 	  to limit number of peripheral access calls.
 
+config SHELL_PRINTF_AUTOFLUSH
+	bool "Indicate if the buffer should be automatically flushed"
+	default y
+	help
+	  Specify whether the shell's printing functions should automatically
+	  flush the printf buffer.
+
 config SHELL_DEFAULT_TERMINAL_WIDTH
 	int "Default terminal width"
 	default 80