On RoCE-capable Thor2, attach fails with
HWRM_FUNC_BACKING_STORE_CFG_V2 returning INVALID_PARAMS, as MRAV is
sized the pre-V2 way and the firmware's AV split value is sent as is.
Size MRAV from the AV split entry, and move the legacy entry-count
packing into bnxt_hwrm_func_backing_store_cfg().
Fixes: d5ce906da7c5 ("bnxt_en: Add backing store V2 support")