habanalabs: debugfs support for larger I2C transactions

I2C debugfs support is limited to 1 byte. We extend functionality
to more than 1 byte by using one of the pad fields as a length.
No backward compatibility issues as new F/W versions will treat 0
length as a 1 byte length transaction.

Signed-off-by: Ofir Bitton <obitton@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>