net: ethtool: Add support for writing firmware blocks using EPL payload

In the CMIS specification for pluggable modules, LPL (Local Payload) and
EPL (Extended Payload) are two types of data payloads used for managing
various functions and features of the module.

EPL payloads are used for more complex and extensive management
functions that require a larger amount of data, so writing firmware
blocks using EPL is much more efficient.

Currently, only LPL payload is supported for writing firmware blocks to
the module.

Add support for writing firmware block using EPL payload, both to
support modules that supports only EPL write mechanism, and to optimize
the flashing process of modules that support LPL and EPL.

Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>