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/ea20_defconfig b/configs/ea20_defconfig
index 7332909..497e551 100644
--- a/configs/ea20_defconfig
+++ b/configs/ea20_defconfig
@@ -33,6 +33,7 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SYS_NS16550=y
+CONFIG_SPI=y
 CONFIG_DAVINCI_SPI=y
 CONFIG_VIDEO=y
 # CONFIG_VIDEO_SW_CURSOR is not set