Convert CONFIG_CMD_EEPROM et al to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_EEPROM
   CONFIG_CMD_EEPROM_LAYOUT
   CONFIG_EEPROM_LAYOUT_HELP_STRING

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
[trini: Rework Kconfig logic slightly, define EEPROM location on TI eval
platforms]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/am335x_sl50_defconfig b/configs/am335x_sl50_defconfig
index 994540d..bae1dfe 100644
--- a/configs/am335x_sl50_defconfig
+++ b/configs/am335x_sl50_defconfig
@@ -26,6 +26,7 @@
 # CONFIG_AUTOBOOT is not set
 # CONFIG_CMD_IMLS is not set
 CONFIG_CMD_ASKENV=y
+CONFIG_CMD_EEPROM=y
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_GPT=y
 CONFIG_CMD_MMC=y