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.

Acked-by: Michael Durrant <mdurrant@arcturusnetworks.com>
Acked-by: Oleksandr Zhadan <oleks@arcturusnetworks.com>
Acked-by: Oleksandr Zhadan and Michael Durrant <arcsupport@arcturusnetworks.com>
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>