wil6210: fix remaining use of non-cached copy of tx/rx descriptors

- Introduce common code for Tx/Rx descriptor physical address set/parse
- Fix endianness for address fields
- consistent descriptor naming: '_d' for non-cached memory, 'd' for cached copy
- wil_tx_desc_map now modify cached copy, no need for 'volatile'

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>