i2c: mlxcpld: Add support for extended transaction length for i2c-mlxcpld

It adds support for extended length of read and write transactions.
New CPLD logic allows double size of the read and write transactions
length. This feature is verified through capability register, which is
renamed from unclear LPF_REG to CPBLTY_REG. Two bits 5 and 6 of these
register are used for length capability detection, while only 01
combination indicates support of extended transaction length.
Others mean lack of such support.

Signed-off-by: Michael Shych <michaelsh@mellanox.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>