lib: utils: Move fdt fixup helper routines to a different file

FDT helper file contain both fdt fixup and parsing functions.

Split the fixup related functions to a separate file for a better code
organization.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>

platform/qemu/virt/platform.c

@@ -14,7 +14,7 @@
 #include <sbi/sbi_const.h>
 #include <sbi/sbi_hart.h>
 #include <sbi/sbi_platform.h>
-#include <sbi_utils/fdt/fdt_helper.h>
+#include <sbi_utils/fdt/fdt_fixup.h>
 #include <sbi_utils/irqchip/plic.h>
 #include <sbi_utils/serial/uart8250.h>
 #include <sbi_utils/sys/clint.h>