Mellanox: Add new mlxsw_spectrum firmware xx.2008.2018

Add latest verified version of Mellanox Spectrum-family switch firmware,
for Spectrum (13.2008.2018), Spectrum-2 (29.2008.2018) and Spectrum-3
(30.2008.2018).

This release fixes the following issues (among others):

- Prioritization of trapped control traffic on Spectrum-2 and Spectrum-3.
- Several edge cases where the FW could get stuck on Spectrum-2 and
  Spectrum-3.
- FW flash issues on Spectrum-3
- Apparent resource exhaustion on Spectrum-3 due to wrong fencing.
- When trapping dropped packets from several TCs, they would only get
  reported under one TC.
- Incorrect rejection of RIF counters with indices over 16 bits.
- An issue where port split might fail after port saw heavy traffic.
- Certain large policer CIR caused effective zero CIR.
- A race that would cause drops due to lack of buffer space.

And includes the following new features:

- Support for shared port headroom
- A new trap for L2 IPv6 DHCP traffic
- On Spectrum-2 and Spectrum-3, support ACL actions that perform ALU
  operations between packet fields, immediate values and general-purpose
  registers
- Early support for 8-way port split on Spectrum-3

Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>