disk: convert CONFIG_ISO_PARTITION to Kconfig

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay73@gmail.com>
diff --git a/configs/pb1000_defconfig b/configs/pb1000_defconfig
index 5a7fa80..a84a434 100644
--- a/configs/pb1000_defconfig
+++ b/configs/pb1000_defconfig
@@ -14,3 +14,4 @@
 CONFIG_CMD_DHCP=y
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y
+# CONFIG_ISO_PARTITION is not set