configs: powerpc: add usb (host) mass storage support

commit 0cfccb54014b ("configs: Resync with savedefconfig")
removed CONFIG_USB_STORAGE from some powerpc platforms' defconfig
files, whicih would block the use case of system loading rootfs
from USB drives, add them back.

Signed-off-by: Ran Wang <ran.wang_1@nxp.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/configs/P2020RDB-PC_36BIT_defconfig b/configs/P2020RDB-PC_36BIT_defconfig
index 08f7012..68ccadb 100644
--- a/configs/P2020RDB-PC_36BIT_defconfig
+++ b/configs/P2020RDB-PC_36BIT_defconfig
@@ -77,5 +77,6 @@
 CONFIG_SPI=y
 CONFIG_FSL_ESPI=y
 CONFIG_USB=y
+CONFIG_USB_STORAGE=y
 CONFIG_DM_USB=y
 CONFIG_ADDR_MAP=y