cmd: nand/sf: isolate legacy code

The 'sf' command is not supposed to rely on the MTD stack, but both
'sf' and 'nand' commands use helpers located in mtd_uboot.c. Despite
their location, these functions do not depend at all on the MTD
stack.

This file (drivers/mtd/mtd_uboot.c) is only compiled if CONFIG_MTD is
selected, which is inconsistent with the current situation. Solve this
by moving these three functions (which are only used by the above two
commands) out of mtd_uboot.c and put them in a C file only compiled
with cmd/sf.c and cmd/nand.c.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
[trini: Don't export get_part function now]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/cmd/Makefile b/cmd/Makefile
index f823d16..36b3cec 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -97,6 +97,9 @@
 obj-$(CONFIG_MP) += mp.o
 obj-$(CONFIG_CMD_MTD) += mtd.o
 obj-$(CONFIG_CMD_MTDPARTS) += mtdparts.o
+ifneq ($(CONFIG_CMD_NAND)$(CONFIG_CMD_SF),)
+obj-y += legacy-mtd-utils.o
+endif
 obj-$(CONFIG_CMD_NAND) += nand.o
 obj-$(CONFIG_CMD_NET) += net.o
 obj-$(CONFIG_CMD_NVEDIT_EFI) += nvedit_efi.o