i2c: mvtwsi: Make address length variable

The length of the address parameter of the __twsi_i2c_read and
__twsi_i2c_write functions is fixed to four bytes.

As a final step in the preparation of the DM conversion, we make the
length of this parameter variable by turning it into an array of bytes,
and convert the 32 bit value that's passed to the legacy functions into
a four-byte-array on the fly.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Stefan Roese <sr@denx.de>