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_dataflash_mmc_mux.c

@@ -0,0 +1,48 @@
+/*
+ * (C) Copyright 2000
+ * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <command.h>
+
+static int mmc_nspi (const char *);
+
+int do_dataflash_mmc_mux (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+{
+	switch (argc) {
+	case 2:			/* on / off	*/
+		switch (mmc_nspi (argv[1])) {
+		case 0:	AT91F_SelectSPI ();
+			break;
+		case 1:	AT91F_SelectMMC ();
+			break;
+		}
+	case 1:			/* get status */
+		printf ("Mux is configured to be %s\n",
+			AT91F_GetMuxStatus () ? "MMC" : "SPI");
+		return 0;
+	default:
+		return CMD_RET_USAGE;
+	}
+	return 0;
+}
+
+static int mmc_nspi (const char *s)
+{
+	if (strcmp (s, "mmc") == 0) {
+		return 1;
+	} else if (strcmp (s, "spi") == 0) {
+		return 0;
+	}
+	return -1;
+}
+
+U_BOOT_CMD(
+	dataflash_mmc_mux, 2, 1, do_dataflash_mmc_mux,
+	"enable or disable MMC or SPI\n",
+	"[mmc, spi]\n"
+	"    - enable or disable MMC or SPI"
+);