net: hix5hd2_gmac: fix compatible strings name

The SoC hix5hd2 compatible string has the suffix "-gmac" and
we should not change its compatible string.
So we should name all the compatible string with the suffix "-gmac".
Creating a new name suffix "-gemac" is unnecessary.

We also add another SoC compatible string in dt binding documentation
and describe which generic version the SoC belongs to.

Fixes: d0fb6ba7

 ("net: hix5hd2_gmac: add generic compatible string")
Signed-off-by: Dongpo Li <lidongpo@hisilicon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>