bnxt_en: Introduce rss ctx structure, alloc/free functions

Add struct bnxt_rss_ctx, related storage lists, required
defines, and its alloc/free functions.

Later patches will use them in order to support multiple
RSS contexts.

Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20240325222902.220712-6-michael.chan@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>