rtwn(4), urtwn(4): merge common code, add support for 11ac devices.

All devices:

• add support for rate adaptation via ieee80211_amrr(9);
• use short preamble for transmitted frames when needed;
• multi-bss support:
  • for RTL8821AU: 2 VAPs at the same time;
  • other: 1 any VAP + 1 sta VAP.

RTL8188CE:

• fix IQ calibration bug (reason of significant speed degradation);
• add h/w crypto acceleration support.

USB:

• A-MPDU Tx support;
• short GI support;

Other:

• add support for RTL8812AU / RTL8821AU chipsets

(a/b/g/n only; no ac yet);

• split merged code into subparts:
  • bus glue (usb/*, pci/*, rtl*/usb/*, rtl*/pci/*)
  • common (if_rtwn*)
  • chip-specific (rtl*/*)
• various other bugfixes.

Due to code reorganization, module names / requirements were changed too:
urtwn urtwnfw -> rtwn rtwn_usb rtwnfw
rtwn rtwnfw -> rtwn rtwn_pci rtwnfw

Tested with RTL8188CE, RTL8188CUS, RTL8188EU and RTL8821AU.

Tested by: kevlo, garga,

		Peter Garshtja <peter.garshtja@ambient-md.com>,
		Kevin McAleavey <kevin.mcaleavey@knosproject.com>,
		Ilias-Dimitrios Vrachnis <id@vrachnis.com>,
		<otacilio.neto@bsd.com.br>

Relnotes: yes