USB: net2280: update dma buffer allocation

This updates the code handling dma-coherent buffer allocations, basically
reusing code from the musb_hdrc driver.  Instead of trying to work around two
significant limitations of the dma framework (memory wastage for buffers
smaller than a page, and inconsistency between calling context requirements
for allocation and free) this just works around one of them (the latter).

So count this as two steps forward (bugfixes:  the latter issue could cause
errors on some platforms, and some MIPS changes broke code for the former), 
and one step back (increasing cross-platform memory wastage).

Plus linelength and whitespace fixes; and minor data segment shrinkage.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>