FDT: only call boot_get_fdt from generic code

All arches except nios2 and microblaze call boot_get_fdt
from bootm_start in common/cmd_bootm.c.

Having nios2 and microblaze do so as well removes code from
their respective do_bootm_linux routines and allows removal of
a nasty ifdef from bootm_start.

In the case where boot_get_fdt returns an error bootm_start
returns and the platform specific do_bootm_linux routines
will never get called.

Also only check argv[3] for an fdt addr if argc > 3 first.
This is already the case for nios2.

Signed-off-by: John Rigby <john.rigby@linaro.org>
CC: Scott McNutt <smcnutt@psyent.com>
CC: Michal Simek <monstr@monstr.eu>
CC: Thomas Chou <thomas@wytron.com.tw>
Acked-by: Wolfgang Denk <wd@denx.de>
Acked-by: Michal Simek <monstr@monstr.eu>
Tested-by: Thomas Chou <thomas@wytron.com.tw>
diff --git a/arch/microblaze/lib/bootm.c b/arch/microblaze/lib/bootm.c
index 8e2c6d8..9f6d6d6 100644
--- a/arch/microblaze/lib/bootm.c
+++ b/arch/microblaze/lib/bootm.c
@@ -46,12 +46,9 @@
 
 	char	*of_flat_tree = NULL;
 #if defined(CONFIG_OF_LIBFDT)
-	ulong	of_size = 0;
-
-	/* find flattened device tree */
-	ret = boot_get_fdt (flag, argc, argv, images, &of_flat_tree, &of_size);
-	if (ret)
-		return 1;
+	/* did generic code already find a device tree? */
+	if (images->ft_len)
+		of_flat_tree = images->ft_addr;
 #endif
 
 	theKernel = (void (*)(char *, ulong, ulong))images->ep;
@@ -64,9 +61,8 @@
 
 	show_boot_progress (15);
 
-	if (!(ulong) of_flat_tree)
-		of_flat_tree = (char *)simple_strtoul (argv[3], NULL, 16);
-
+	if (!of_flat_tree && argc > 3)
+		of_flat_tree = (char *)simple_strtoul(argv[3], NULL, 16);
 #ifdef DEBUG
 	printf ("## Transferring control to Linux (at address 0x%08lx) " \
 				"ramdisk 0x%08lx, FDT 0x%08lx...\n",