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/configs/Colombus_defconfig b/configs/Colombus_defconfig
index ac97501..f479d75 100644
--- a/configs/Colombus_defconfig
+++ b/configs/Colombus_defconfig
@@ -17,6 +17,8 @@
 CONFIG_VIDEO_LCD_PANEL_I2C_SCL="PA24"
 CONFIG_VIDEO_LCD_PANEL_EDP_4_LANE_1620M_VIA_ANX9804=y
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
+CONFIG_SYS_I2C_LEGACY=y
+CONFIG_SPL_SYS_I2C_LEGACY=y
 CONFIG_SYS_I2C_SOFT=y
 CONFIG_SYS_I2C_SOFT_SPEED=50000
 CONFIG_SYS_I2C_SOFT_SLAVE=0x00