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/cmd/eeprom.c b/cmd/eeprom.c
index c61b396..7608be1 100644
--- a/cmd/eeprom.c
+++ b/cmd/eeprom.c
@@ -68,7 +68,7 @@
 void eeprom_init(int bus)
 {
 	/* SPI EEPROM */
-#if defined(CONFIG_SPI) && !defined(CONFIG_ENV_EEPROM_IS_ON_I2C)
+#if defined(CONFIG_MPC8XX_SPI) && !defined(CONFIG_ENV_EEPROM_IS_ON_I2C)
 	spi_init_f();
 #endif
 
@@ -131,7 +131,7 @@
 	int ret = 0;
 
 	/* SPI */
-#if defined(CONFIG_SPI) && !defined(CONFIG_ENV_EEPROM_IS_ON_I2C)
+#if defined(CONFIG_MPC8XX_SPI) && !defined(CONFIG_ENV_EEPROM_IS_ON_I2C)
 	if (read)
 		spi_read(addr, alen, buffer, len);
 	else