Merge branch 'stmmac-DMA-burst'

Niklas Cassel says:

====================
net: stmmac: make DMA programmable burst length more configurable

Make DMA programmable burst length more configurable in the stmmac driver.

This is done by adding support for independent pbl for tx/rx through DT.
More fine grained tuning of pbl is possible thanks to a DT property saying
that we should NOT multiply pbl values by x8/x4 in hardware.

All new DT properties are optional, and created in a way that it will not
affect any existing DT configurations.

Changes since V1:
Created cover-letter.
Rebased patch set against next-20161205, since conflicting patches to
stmmac_platform.c has been merged since V1.

Changes since V2:
Moved default value initialization of pbl to stmmac_platform.c
and added a check for pbl != 0 in stmmac_main.c,
to catch a possble pbl == 0 from pci glue.
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Signed-off-by: David S. Miller <davem@davemloft.net>