cmd: thordown: Add proper dependency for CMD_THOR_DOWNLOAD

When CONFIG_CMD_USB and CONFIG_USB are disabled some compilation errors are seen as below.

cmd/thordown.o: in function `usb_gadget_initialize':
include/linux/usb/gadget.h:981: undefined reference to `board_usb_init'
cmd/thordown.o: in function `do_thor_down':
cmd/thordown.c:68: undefined reference to `g_dnl_unregister'
cmd/thordown.o: in function `usb_gadget_release':
include/linux/usb/gadget.h:986: undefined reference to `board_usb_cleanup'
cmd/thordown.o: in function `do_thor_down':
cmd/thordown.c:41: undefined reference to `g_dnl_register'
cmd/thordown.c:48: undefined reference to `thor_init'
cmd/thordown.c:56: undefined reference to `thor_handle'
gnu/aarch64/lin/aarch64-linux/bin/aarch64-linux-gnu-ld.bfd: line 4:  8485
Segmentation fault      (core dumped) $CC --sysroot=$LIBC
--no-warn-rwx-segment "$@"
Makefile:1779: recipe for target 'u-boot' failed
make: *** [u-boot] Error 139
make: *** Deleting file 'u-boot'

Add dependency of USB_GADGET_DOWNLOAD for CONFIG_CMD_THOR_DOWNLOAD to fix the errors.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@amd.com>
Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Link: https://lore.kernel.org/r/20230904031528.11817-2-venkatesh.abbarapu@amd.com


Signed-off-by: Michal Simek <michal.simek@amd.com>