sh: Remove r7780mp board

This board has not been converted to CONFIG_DM by the deadline of v2020.01
and is missing other conversions which depend on this as well.  Remove it.

Patch-cc: Nobuhiro Iwamatsu <iwamatsu.nobuhiro@renesas.com>
Patch-cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Signed-off-by: Tom Rini <trini@konsulko.com>