ppc: Remove UCP1020 board

This board has not been converted to CONFIG_DM_PCI by the deadline.
Remove it.

Note that we have to add CONFIG_SPIFLASH to scripts/config_whitelist.txt
because it's not really migrated at this point.

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Handle CONFIG_SPIFLASH differently and delete Kconfig file]
Signed-off-by: Tom Rini <trini@konsulko.com>