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/MPC8349EMDS_SLAVE_defconfig b/configs/MPC8349EMDS_SLAVE_defconfig
index 2b7d2fd..4594982 100644
--- a/configs/MPC8349EMDS_SLAVE_defconfig
+++ b/configs/MPC8349EMDS_SLAVE_defconfig
@@ -99,6 +99,7 @@
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_ENV_ADDR=0xFE080000
 CONFIG_ENV_ADDR_REDUND=0xFE0A0000
+CONFIG_SYS_I2C_LEGACY=y
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_FLASH_CFI_DRIVER=y