[SRU][Precise][Trusty][Vivid][Wily]xhci: Workaround to get Intel xHCI reset working more reliably

[Zhang, Xiong Y]

Buglink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1518816

 SRU Justification:
 On all of Intel's shipping xHCI platforms, including both servers and clients, the controller can cause the shutdown process to hang.
 This is because existing Intel xHCI controllers require a delay of 1 mS,after setting the CMD_RESET bit in command register, before accessing any HC registers. This allows the HC to complete the reset operation and be ready for HC register access.
Fix:
Patch in 4.4-rc2 and cc stable kernel
commit a5964396190d0c40dd549c23848c282fffa5d1f2
Author: Rajmohan Mani <rajmohan.mani at intel.com>
Date: Wed Nov 18 10:48:20 2015 +0200
    xhci: Workaround to get Intel xHCI reset working more reliably
Regression Potential: Just 1ms delay for xhci_reset, so regressions are very unlikely.
thanks

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