Convert CONFIG_OMAP3_SPI to Kconfig

This converts the following to Kconfig:
   CONFIG_OMAP3_SPI

Signed-off-by: Adam Ford <aford173@gmail.com>
[trini: Minor comment tweaks]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/ti816x_evm_defconfig b/configs/ti816x_evm_defconfig
index bc1f7c8..9106a05 100644
--- a/configs/ti816x_evm_defconfig
+++ b/configs/ti816x_evm_defconfig
@@ -42,4 +42,5 @@
 CONFIG_MMC_OMAP_HS=y
 CONFIG_NAND=y
 CONFIG_SYS_NS16550=y
+CONFIG_OMAP3_SPI=y
 # CONFIG_USE_PRIVATE_LIBGCC is not set