sh: espt-giga board support

This adds support for the ESPT-Giga (Ethernet Serial Parallel
Translator) SH7763-based reference board.

Board support is relatively sparse, presently supporting serial,
gigabit ethernet, USB host, and MTD.

More information (in Japanese) available at:

	http://www.cente.jp/product/cente_hard/ESPT-Giga.html

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu.nobuhiro@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>