bnxt_en: Add helper function bnxt_hwrm_vnic_rss_cfg_p5()

This is a pure refactoring patch.  The new function
bnxt_hwrm_vnic_set_rss_p5() will set up the P5_PLUS specific RSS ring
table and then call bnxt_hwrm_vnic_cfg() to setup the vnic for proper
RSS operations.  This new function will be used later for additional
RSS contexts.

Signed-off-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20240325222902.220712-4-michael.chan@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>