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/tqc/tqma6/tqma6.c b/board/tqc/tqma6/tqma6.c
index 4f86a92..0d8229d 100644
--- a/board/tqc/tqma6/tqma6.c
+++ b/board/tqc/tqma6/tqma6.c
@@ -171,7 +171,7 @@
 #endif
 #endif
 
-#ifdef CONFIG_SYS_I2C_LEGACY
+#if CONFIG_IS_ENABLED(SYS_I2C_LEGACY)
 static struct i2c_pads_info tqma6_i2c3_pads = {
 	/* I2C3: on board LM75, M24C64,  */
 	.scl = {
@@ -216,7 +216,7 @@
 #ifndef CONFIG_DM_SPI
 	tqma6_iomuxc_spi();
 #endif
-#ifdef CONFIG_SYS_I2C_LEGACY
+#if CONFIG_IS_ENABLED(SYS_I2C_LEGACY)
 	tqma6_setup_i2c();
 #endif