i2c: i801: Split i801_block_transaction

i2c and smbus block transaction handling have little in common,
therefore split this function to improve code readability.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>