iwlwifi: move tid_to_ac to PCI-E

Currently, queue mapping is handled in the
transport. This may change, but until then
the code for it can be close to where it's
used rather than in iwl-shared.h.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>