i2c: Rename CONFIG_SYS_I2C to CONFIG_SYS_I2C_LEGACY

It is quite confusing that CONFIG_SYS_I2C selects the legacy I2C and
CONFIG_DM_I2C selects the current I2C. The deadline to migrate I2C is less
than a year away.

Also we want to have a CONFIG_I2C for U-Boot proper just like we have
CONFIG_SPL_I2C for SPL, so we can simplify the Makefile rules.

Rename this symbol so it is clear it is going away.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/arch/arm/include/asm/arch-fsl-layerscape/config.h b/arch/arm/include/asm/arch-fsl-layerscape/config.h
index da7ca05..3675ce7 100644
--- a/arch/arm/include/asm/arch-fsl-layerscape/config.h
+++ b/arch/arm/include/asm/arch-fsl-layerscape/config.h
@@ -184,7 +184,7 @@
 #define TZPC_BASE				0x02200000
 #define TZPCDECPROT_0_SET_BASE			(TZPC_BASE + 0x804)
 #if !CONFIG_IS_ENABLED(DM_I2C)
-#define CONFIG_SYS_I2C
+#define CONFIG_SYS_I2C_LEGACY
 #define CONFIG_SYS_I2C_EARLY_INIT
 #endif
 #define SRDS_MAX_LANES  8