arm: Remove ot1200 board

This board relies on using CONFIG_LIBATA but does not enable CONFIG_AHCI.  The
deadline for this conversion was the v2019.07 release.  In order to
convert to using the DWC SATA driver under DM further migrations are
required.

Cc: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Acked-by: Christian Gmeiner <christian.gmeiner@gmail.com>