[TG3]: Endianness annotations.

Fixed misannotations, introduced a new helper - tg3_nvram_read_le().
It gets __le32 * instead of u32 * and puts there the value converted
to little-endian.  A lot of callers of tg3_nvram_read() were doing
that; converted them to tg3_nvram_read_le().

At that point the driver is practically endian-clean; the only remaining
place is an actual bug, AFAICS; will be dealt with in the next patch.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>