Rename the low-level functions from iic_tpm_read/write to
cr50_i2c_read/write to better match the driver name, and pass in the
tpm_chip structure to the low-level read/write functions as it will
be needed in future changes.
BUG=chrome-os-partner:53336
Change-Id: Ib4a68ce1b3a83ea7c4bcefb9c6f002f6dd4aac1f
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>