cxgb4: Support CPL_SGE_EGR_UPDATEs encapsulated in a CPL_FW4_MSG

Newer firmware can post CPL_SGE_EGR_UPDATE message encapsulated in a
CPL_FW4_MSG as follows

flit0 rss_header (if DropRSS == 0 in IQ context)
flit1 CPL_FW4_MSG cpl
flit2 rss_header w/opcode CPL_SGE_EGR_UPDATE
flit3 CPL_SGE_EGR_UPDATE cpl

So FW4_MSG CPLs with a newly created type of FW_TYPE_RSSCPL have the
CPL_SGE_EGR_UPDATE CPL message in flit 2 of the FW4_MSG. Firmware can still
post regular CPL_SGE_EGR_UPDATE messages, so the drivers need to handle
both.

This patch also writes a new parameter to firmware requesting encapsulated
EGR_UPDATE. This allows firmware with this support to not break older drivers.

Signed-off-by: Vipul Pandya <vipul@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>