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/board/renesas/draak/draak.c b/board/renesas/draak/draak.c
index 3d00652..71efeaf 100644
--- a/board/renesas/draak/draak.c
+++ b/board/renesas/draak/draak.c
@@ -38,7 +38,7 @@
 
 int board_early_init_f(void)
 {
-#if defined(CONFIG_SYS_I2C_LEGACY) && defined(CONFIG_SYS_I2C_SH)
+#if CONFIG_IS_ENABLED(SYS_I2C_LEGACY) && defined(CONFIG_SYS_I2C_SH)
 	/* DVFS for reset */
 	mstp_clrbits_le32(SMSTPCR9, SMSTPCR9, DVFS_MSTP926);
 #endif