MFC r343269, r346567

r343269:
cxgbe(4): Allow negative values in hw.cxgbe.fw_install and take them to
mean that the driver should taste the firmware in the KLD and use that
firmware's version for all its fw_install checks.

The driver gets firmware version information from compiled-in values by
default and this change allows custom (or older/newer) firmware modules
to be used with the stock driver.

There is no change in default behavior.

Sponsored by: Chelsio Communications

r346567:
cxgbe(4): Make sure bundled_fw is always initialized before use.

This fixes a bug that prevented the driver from auto-flashing the
firmware when it didn't see one on the card. This feature was
introduced in r321390 and this bug was introduced in r343269.

Reported by: gallatin@
Sponsored by: Chelsio Communications