bng_en: add HW stats infra and structured ethtool ops

bng_en: add HW stats infra and structured ethtool ops

Implement the hardware-level statistics foundation and modern structured
ethtool operations.

1. Infrastructure: Add HWRM firmware wrappers (FUNC_QSTATS_EXT,
   PORT_QSTATS_EXT, and PORT_QSTATS) to query ring and port counters.
2. Structured ops: Implement .get_eth_phy_stats, .get_eth_mac_stats,
   .get_eth_ctrl_stats, .get_pause_stats, and .get_rmon_stats.

Stats are initially reported as 0; accumulation logic is added
in a subsequent patch.

Signed-off-by: Bhargava Marreddy <bhargava.marreddy@broadcom.com>
Reviewed-by: Vikas Gupta <vikas.gupta@broadcom.com>
Link: https://patch.msgid.link/20260406180420.279470-7-bhargava.marreddy@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>