libfdt: Introduce new ARCH_FIXUP_FDT option

Add new Kconfig option to disable arch_fixup_fdt() calls for cases where
U-Boot shouldn't update memory setup in DTB file.
One example of usage of this option is to boot OS with different memory
setup than U-Boot use.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/mips/lib/bootm.c b/arch/mips/lib/bootm.c
index aa0475a..0c6a4ab 100644
--- a/arch/mips/lib/bootm.c
+++ b/arch/mips/lib/bootm.c
@@ -253,6 +253,7 @@
 #endif
 }
 
+#ifdef CONFIG_ARCH_FIXUP_FDT
 int arch_fixup_fdt(void *blob)
 {
 #if CONFIG_IS_ENABLED(MIPS_BOOT_FDT) && CONFIG_IS_ENABLED(OF_LIBFDT)
@@ -264,6 +265,7 @@
 	return 0;
 #endif
 }
+#endif
 
 static int boot_setup_fdt(bootm_headers_t *images)
 {