net: designware: Fix alignment of buffer descriptors

It's important that buffer descriptors are aligned in accordance to GMAC
data bus width (32/64/128-bit). It's safe to align to 128-bit (16-bytes)
for every bus width type.

If buffer descriptor is improperly aligned GMAC discards lower bits of
provided address and as a result reads from improper location that
doesn't match expected fields.

Commit ef76025a "net: Multiple
updates/enhancements to designware.c" introduced another structure
member "link_printed" right before buffer descriptors while "padding"
member was left untouched. This together with alignment of structure
itself to 16-byte boundary forces buffer descriptoprs always to be
4-byte aligned that causes driver complete disfunction if GMAC bus width
is 64 or 128-bit.

Proposed change makes sure all buffer descriptors are 16-byte (128-bit)
aligned.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Patch: 277902