Move all command code into its own directory

There are a lot of unrelated files in common, including all of the commands.
Moving them into their own directory makes them easier to find and is more
logical.

Some commands include non-command code, such as cmd_scsi.c. This should be
sorted out at some point so that the function can be enabled with or without
the associated command.

Unfortunately, with m68k I get this error:

m68k:  +   M5329AFEE
+arch/m68k/cpu/mcf532x/start.o: In function `_start':
+arch/m68k/cpu/mcf532x/start.S:159:(.text+0x452): relocation truncated to fit: R_68K_PC16 against symbol `board_init_f' defined in .text.board_init_f section in common/built-in.o

I hope someone can shed some light on what this means. I hope it isn't
depending on the position of code in the image.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Acked-by: Stefan Roese <sr@denx.de>
Acked-by: Przemyslaw Marczak <p.marczak@samsung.com>

cmd/cmd_diag.c

@@ -0,0 +1,60 @@
+/*
+ * (C) Copyright 2002
+ * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+/*
+ * Diagnostics support
+ */
+#include <common.h>
+#include <command.h>
+#include <post.h>
+
+int do_diag (cmd_tbl_t * cmdtp, int flag, int argc, char * const argv[])
+{
+	unsigned int i;
+
+	if (argc == 1 || strcmp (argv[1], "run") != 0) {
+		/* List test info */
+		if (argc == 1) {
+			puts ("Available hardware tests:\n");
+			post_info (NULL);
+			puts ("Use 'diag [<test1> [<test2> ...]]'"
+					" to get more info.\n");
+			puts ("Use 'diag run [<test1> [<test2> ...]]'"
+					" to run tests.\n");
+		} else {
+			for (i = 1; i < argc; i++) {
+			    if (post_info (argv[i]) != 0)
+				printf ("%s - no such test\n", argv[i]);
+			}
+		}
+	} else {
+		/* Run tests */
+		if (argc == 2) {
+			post_run (NULL, POST_RAM | POST_MANUAL);
+		} else {
+			for (i = 2; i < argc; i++) {
+			    if (post_run (argv[i], POST_RAM | POST_MANUAL) != 0)
+				printf ("%s - unable to execute the test\n",
+					argv[i]);
+			}
+		}
+	}
+
+	return 0;
+}
+/***************************************************/
+
+U_BOOT_CMD(
+	diag,	CONFIG_SYS_MAXARGS,	0,	do_diag,
+	"perform board diagnostics",
+	     "    - print list of available tests\n"
+	"diag [test1 [test2]]\n"
+	"         - print information about specified tests\n"
+	"diag run - run all available tests\n"
+	"diag run [test1 [test2]]\n"
+	"         - run specified tests"
+);