[PATCH v6] Align tegra-ehci DMA transfers to 32B

[Robert Morell]

This small set of patches fixes an issue where DMA from the tegra EHCI
controller could be corrupted.  It was most commonly seen with USB network
adapters, though in theory it could happen with any USB traffic.

Note: An attempt was made to fix this specifically for network devices with
commit 367c3aab, which set NET_IP_ALIGN to 0 and NET_SKB_PAD to 32.
Unfortunately, not all network drivers honor them (presumably since these are
intended as optimizations rather than hard rules).  This does mean that
properly behaved network drivers should fall through this code with very little
overhead, however.

Version 2 of this patchset gets rid of the HCD placeholder in the flags and
instead simply reserves the flag globally for this use.

Version 3 makes the hook definition and commit message much more verbose, and
moves the new flag from the second patch to the first.

Version 4 adds logic to prevent data copy-out on failure.

Version 5 rebases against linux-tegra-2.6.37.

Version 6 renames the map/unmap exported functions from the hcd core to have
usb_hcd prefixes as an additional patch.  It also fixes some comment
formatting, and removes the logic added in version 4 to skip the memcpy from
the temp buffer on failure (some data may still be good).

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