Convert CONFIG_SYS_I2C_LEGACY to Kconfig and add CONFIG_[ST]PL_SYS_I2C_LEGACY

First, we convert CONFIG_SYS_I2C_LEGACY to Kconfig.  Next, as you cannot
have SYS_I2C_LEGACY and DM_I2C at the same time, introduce
CONFIG_SPL_SYS_I2C_LEGACY so that we can enable the legacy option only
in SPL.  Finally, for some PowerPC cases we also need
CONFIG_TPL_SYS_I2C_LEGACY support.  Convert all of the existing users to
one or more symbols.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/colibri_pxa270.h b/include/configs/colibri_pxa270.h
index 6889e8b..15cbd23 100644
--- a/include/configs/colibri_pxa270.h
+++ b/include/configs/colibri_pxa270.h
@@ -41,7 +41,7 @@
  */
 
 /* I2C support */
-#ifdef CONFIG_SYS_I2C_LEGACY
+#if CONFIG_IS_ENABLED(SYS_I2C_LEGACY)
 #define CONFIG_SYS_I2C_PXA
 #define CONFIG_PXA_STD_I2C
 #define CONFIG_PXA_PWR_I2C