i2c-algo-bit: Emulate SMBus block read

Now that i2c-core lets the i2c bus drivers emulate the SMBus block read
and SMBus block process call transaction types, let's implement that in
the popular i2c bit-banging driver. This will also act as a reference
implementation for other bus drivers which want to do the same.

Signed-off-by: Jean Delvare <khali@linux-fr.org>