net/bnxt: use enum for bank ID

net/bnxt: use enum for bank ID

Instead of integer, using enum tf_sram_bank_id for bank
id in tf_set_sram_policy_parms.

Add index check against the allocation of the meter
instance for meter drop count because there is no
reason to access it if the corresponding meter
entry is not allocated.

Signed-off-by: Jay Ding <jay.ding@broadcom.com>
Reviewed-by: Steve Rempe <steve.rempe@broadcom.com>
Reviewed-by: Farah Smith <farah.smith@broadcom.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>