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/salvator-x/salvator-x.c b/board/renesas/salvator-x/salvator-x.c
index d4752e5..c27eb3f 100644
--- a/board/renesas/salvator-x/salvator-x.c
+++ b/board/renesas/salvator-x/salvator-x.c
@@ -37,7 +37,7 @@
 
 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
@@ -75,7 +75,7 @@
 
 void reset_cpu(void)
 {
-#if defined(CONFIG_SYS_I2C_LEGACY) && defined(CONFIG_SYS_I2C_SH)
+#if CONFIG_IS_ENABLED(SYS_I2C_LEGACY) && defined(CONFIG_SYS_I2C_SH)
 	i2c_reg_write(CONFIG_SYS_I2C_POWERIC_ADDR, 0x20, 0x80);
 #else
 	/* only CA57 ? */