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/common/board_f.c b/common/board_f.c
index f274653..3dc0eaa 100644
--- a/common/board_f.c
+++ b/common/board_f.c
@@ -244,7 +244,7 @@
 	return 0;
 }
 
-#if defined(CONFIG_SYS_I2C_LEGACY)
+#if CONFIG_IS_ENABLED(SYS_I2C_LEGACY)
 static int init_func_i2c(void)
 {
 	puts("I2C:   ");
@@ -871,7 +871,7 @@
 	misc_init_f,
 #endif
 	INIT_FUNC_WATCHDOG_RESET
-#if defined(CONFIG_SYS_I2C_LEGACY)
+#if CONFIG_IS_ENABLED(SYS_I2C_LEGACY)
 	init_func_i2c,
 #endif
 #if defined(CONFIG_VID) && !defined(CONFIG_SPL)