ibmvnic: store RX and TX subCRQ handle array in ibmvnic_adapter struct

Currently the driver reads RX and TX subCRQ handle array directly from
a DMA-mapped buffer address when it needs to make a H_SEND_SUBCRQ
hcall. This patch stores that information in the ibmvnic_sub_crq_queue
structure instead of reading from the buffer received at login. The
overall goal of this patch is to parse relevant information from the
login response buffer and store it in the driver's private data
structures so that we don't need to read directly from the buffer and
can then free up that memory.

Signed-off-by: Cristobal Forno <cforno12@linux.ibm.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>