net/bnxt: modify context memory allocation

net/bnxt: modify context memory allocation

Newer devices like SR2 may have chip backing store and do not require
host backed memory allocation.

In these cases, HWRM_FUNC_BACKING_STORE_QCAPS will return a zero entry
size to indicate contexts for which the host should not allocate backing
store.

Selectively allocate context memory based on device capabilities and
only enable backing store for the appropriate contexts

Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>