platform/x86: mlx-platform: Add support for new msn274x system type

It adds support for new Mellanox system types of basic class msn274x,
containing system MSN2740 (32x100GbE Ethernet switch with cost reduction)
and its derivatives. These are the Top of the Rack system, equipped with
Mellanox Small Form Factor carrier board and switch board with Mellanox
Spectrum device, which supports Ethernet switching with 32X100G ports line
rate of up to EDR speed.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>