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/pinecube_defconfig b/configs/pinecube_defconfig
index c54958e..b2a8370 100644
--- a/configs/pinecube_defconfig
+++ b/configs/pinecube_defconfig
@@ -8,6 +8,8 @@
 CONFIG_DRAM_ODT_EN=y
 CONFIG_I2C0_ENABLE=y
 CONFIG_SPL_I2C=y
+CONFIG_SYS_I2C_LEGACY=y
+CONFIG_SPL_SYS_I2C_LEGACY=y
 CONFIG_SYS_I2C_MVTWSI=y
 # CONFIG_NETDEVICES is not set
 CONFIG_AXP209_POWER=y