Net: ucc_geth ethernet driver optimization space

[Liu Dave-R63238]

Guys,

The ucc_geth ethernet driver have dozens of strong sync read/write
operation, such as in_be32/16/8, out_be32/16/8.

all of them is sync read/write, it is very expensive for performance.

For the critical patch, we can remove some unnecessary in_be(x),
out_be(x) with normal memory operation, and keep some necessary
memory barrier.

eg: BD access in the interrupt handler and start_xmit.

The BD operation only need the memory barrier between length/buffer
and status.

struct buffer descriptor {
	u16 status;
	u16 length;
	u32 buffer;
} __attribute__ ((packed));

struct buffer descriptor *BD;

BD->length = xxxx;
BD->buffer = yyyy;
wmb();
BD->status = zzzz;

For powerpc, eieio is enough for 60x, mbar 1 is enough for e500.
Of couse, also need the memory clobber to avoid the compiler
reorder between them.

Thanks, Dave