Convert CONFIG_SPI to Kconfig

This converts the following to Kconfig:
   CONFIG_SPI

This partly involves updating code that assumes that CONFIG_SPI implies
things that are specific to the MPC8xx SPI driver.  For now, just update
the CONFIG tests.  This also involves reworking the default for
CONFIG_SYS_DEF_EEPROM_ADDR so that we don't set it when we cannot make a
reasonable default, as it does not cause any compile failures.

Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/am335x_igep003x_defconfig b/configs/am335x_igep003x_defconfig
index 48dc3c9..5f57a67 100644
--- a/configs/am335x_igep003x_defconfig
+++ b/configs/am335x_igep003x_defconfig
@@ -45,6 +45,7 @@
 CONFIG_MTD_UBI_FASTMAP=y
 CONFIG_DRIVER_TI_CPSW=y
 CONFIG_SYS_NS16550=y
+CONFIG_SPI=y
 CONFIG_OMAP3_SPI=y
 CONFIG_FAT_WRITE=y
 CONFIG_OF_LIBFDT=y