arm: Remove spear320 boards

These boards have not been converted to CONFIG_DM_USB by the deadline
and is also missing conversion to CONFIG_DM.  Remove them.  As this is
also the last SPEAR3XX platform, remove that symbol as well.

Cc: Vipin Kumar <vipin.kumar@st.com>
Signed-off-by: Tom Rini <trini@konsulko.com>