tpm: Move the I2C TPM code into one file

The current Infineon I2C TPM driver is written in two parts, intended to
support use with other I2C devices. However we don't have any users and the
Atmel I2C TPM device does not use this file.

We should simplify this and remove the unused abstration. As a first step,
move the code into one file.

Also the name tpm_private.h suggests that the header file is generic to all
TPMs but it is not. Rename it indicate that it relates only to this driver

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>