include/device: Split i2c.h into three

Split `i2c.h` into three pieces to ease reuse of the generic defi-
nitions. No code is changed.

* `i2c.h`        - keeps the generic definitions
* `i2c_simple.h` - holds the current, limited to one controller driver
                   per board, devicetree independent I2C interface
* `i2c_bus.h`    - will become the devicetree compatible interface for
                   native I2C (e.g. non-SMBus) controllers

Change-Id: I382d45c70f9314588663e1284f264f877469c74d
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/20845
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/drivers/i2c/tpm/cr50.c b/src/drivers/i2c/tpm/cr50.c
index 3505dce..baf5fe0 100644
--- a/src/drivers/i2c/tpm/cr50.c
+++ b/src/drivers/i2c/tpm/cr50.c
@@ -36,7 +36,7 @@
 #include <types.h>
 #include <delay.h>
 #include <console/console.h>
-#include <device/i2c.h>
+#include <device/i2c_simple.h>
 #include <endian.h>
 #include <timer.h>
 #include <tpm.h>