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/ap121_defconfig b/configs/ap121_defconfig
index 2d418f6..1eff3ed 100644
--- a/configs/ap121_defconfig
+++ b/configs/ap121_defconfig
@@ -54,6 +54,7 @@
 CONFIG_DEBUG_UART_CLOCK=25000000
 CONFIG_DEBUG_UART_BOARD_INIT=y
 CONFIG_AR933X_UART=y
+CONFIG_SPI=y
 CONFIG_DM_SPI=y
 CONFIG_ATH79_SPI=y
 CONFIG_LZMA=y