bnxt: Update firmware header file with the latest one

hsi_struct_def.h file contains all firmware (HWRM) data struct's, updated
that with the latest one which was released on 30'th Aug.

After this upgrade, HWRM version will be 1.8.1.5 (earlier it was 1.4.0).

Submitted by: Bhargava Chenna Marreddy <bhargava.marreddy@broadcom.com>
Reviewed by: shurd, sbruno
Approved by: sbruno (mentor)
Sponsored by: Broadcom Limited
Differential Revision: https://reviews.freebsd.org/D12203