spi: omap3: Convert to driver model

spi: omap3: Convert to driver model

After this conversion the driver will able to support both dm and non-dm
and code is more extensible like we can remove the non-dm part simply
without touching anycode if all the boards which are using this driver
become dm driven.

Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Christophe Ricard <christophe-h.ricard@st.com>
Tested-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>
[Set priv->wordlen, Add Kconfig entry and file credit for dm conversion]
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>