sh_eth: add more PM methods

Add sh_eth_{suspend|resume}() implementing {suspend|resume|freeze|thaw|poweroff|
restore}() PM methods to make it possible to restore from hibernation not only
in Linux  but also in e.g. U-Boot and  to have more determined state on resume/
restore.

Signed-off-by: Mikhail Ulyanov <mikhail.ulyanov@cogentembedded.com>
[Sergei: moved sh_eth_{suspend|resume}() before sh_eth_runtime_nop(), enclosed
them with #ifdef CONFIG_PM_SLEEP, reordered the local variables, got rid of
*goto* and label, reordered macro invocations, renamed, modified the changelog.]
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>