boot: allow bootmeth-distro without CONFIG_NET

Remove the dependency on CMD_PXE from BOOTMETH_DISTRO by introducing a
new hidden kconfig symbol to control whether pxe_utils is compiled,
allowing bootstd's distro method to be compiled without needing
networking support enabled.

Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Correct build errors when CMD_BOOTM is not enabled:
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/Kconfig b/boot/Kconfig
index eddb0c6..a294ad7 100644
--- a/boot/Kconfig
+++ b/boot/Kconfig
@@ -294,6 +294,12 @@
 
 endif # FIT
 
+config PXE_UTILS
+	bool
+	select MENU
+	help
+	  Utilities for parsing PXE file formats.
+
 config BOOTSTD
 	bool "Standard boot support"
 	default y
@@ -345,7 +351,7 @@
 
 config BOOTMETH_DISTRO
 	bool "Bootdev support for distro boot"
-	depends on CMD_PXE
+	select PXE_UTILS
 	default y
 	help
 	  Enables support for distro boot using bootdevs. This makes the