i2c: fsl_i2c: Migrate to Kconfig

- As there are no boards that use different values for speed / slave on
  different buses, use a single option.
- Switch to using the common SYS_I2C_SPEED / SYS_I2C_SLAVE options.
- Introduce _HAS_ options for additional buses as only the first one is
  common to all users.
- Convert all remaining symbols to Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/MPC8548CDS_legacy_defconfig b/configs/MPC8548CDS_legacy_defconfig
index 5f791dc..26f8ab9 100644
--- a/configs/MPC8548CDS_legacy_defconfig
+++ b/configs/MPC8548CDS_legacy_defconfig
@@ -26,6 +26,7 @@
 CONFIG_ENV_ADDR=0xFFF60000
 CONFIG_DM=y
 CONFIG_DM_I2C=y
+CONFIG_SYS_I2C_FSL=y
 CONFIG_SYS_I2C_EEPROM_ADDR=0x57
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y