bnxt_en: Remove BNXT_RX_HDL and BNXT_TX_HDL

These 2 constants were used for the one RX and one TX completion
ring pointer in the cpr->cp_ring_arr fixed array.  Now that we've
changed to allocating the array for the exact number of entries to
support more TX rings, we no longer use these constants.

The array index as well as the type of completion ring (RX/TX) are
now encoded in the handle for the completion ring.  This will allow
us to locate the completion ring during NAPI for any number of
completion rings sharing the same MSIX.  In the following patches,
we'll be adding support for more TX rings associated with the same
MSIX vector.

Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>