OMAP3_SPI: Kconfig: move OMAP3_SPI out of DM_SPI section.

The OMAP3_SPI driver can work with or without DM_SPI.  Moving this
outside of the #if DM_SPI section allows us to include it on boards
that don't support DM_SPI yet.

Signed-off-by: Adam Ford <aford173@gmail.com>