sh_eth: fix 16-bit descriptor field access endianness too

Commit 1299653a ("sh_eth: fix descriptor access endianness") only
addressed the 32-bit buffer address field byte-swapping  but the driver
still accesses 16-bit frame/buffer length descriptor fields without the
necessary byte-swapping -- which should affect the big-endian kernels.
In order to be able to use {cpu|edmac}_to_{edmac|cpu}(), we need to declare
the RX/TX descriptor word 1 as a 32-bit field and use shifts/masking to
access the 16-bit subfields (which gets rid of the ugly #ifdef'ery too)...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>