bnxt: Add led(4) identification support

[kbowling]

Summary

Query the firmware for the LEDs on each physical port and expose
/dev/led/bnxt* only when alternate blinking is supported.  Configure
every LED in the advertised group for identification and restore its
default firmware state before a function reset.

This is a structural port of DPDK bnxt HWRM identification path,
confirmed against Linux where old hwrm (0x10601) was observed.

Test Plan

I would have to go dig through my tubs-o-NICs at my lab to find suitable HW so this has not been witnessed for sensible LED function.

echo 1 > /dev/led/bnxt0
and sight check is reasonable. Could monitor the registers also.

[gallatin]

LGTM, but holding back approval as I don't feel like I own this driver..

[kbowling]

Committed as 98b5640786f874949e441bee7c4ad5740cd6a649