davinci: add spi devices support for da850/omap-l138/am18x evm

This patch adds the on-board SPI flash device to the
DA850/OMAP-L138/AM18x EVM. It also registers the SPI flash
device to the MTD subsystem.

Based on SPI flash device support for MityDSP-L138F platform.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
[michael.williamson@criticallink.com: moved da850_evm_spi1_pdata to devices-da8xx.c]
[michael.williamson@criticallink.com: moved da850evm_init_spi1 to devices-da8xx.c]
Signed-off-by: Michael Williamson <michael.williamson@criticallink.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>