spi: ich: Some clean up

This cleans up the ich spi driver a little bit:
- Remove struct ich_spi_slave that is not referenced anywhere
- Remove ending period in some comments
- Move struct ich_spi_platdata and struct ich_spi_priv to ich.h
- Add #ifndef _ICH_H_ .. in ich.h

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagan Teki <jteki@openedev.com>