bnxt_en: Report PCIe link speed and width during driver load

Add code to log a message during driver load indicating PCIe link
speed and width.

The log message will look like this:
bnxt_en 0000:86:00.0 eth0: PCIe: Speed 8.0GT/s Width x8

Signed-off-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>