net: phy: broadcom: Add IDDQ-SR mode

Add support for putting the PHY into IDDQ Soft Recovery mode by setting
the TOP_MISC register bits accordingly. This requires us to implement a
custom bcm54xx_suspend() routine which diverges from genphy_suspend() in
order to configure the PHY to enter IDDQ with software recovery as well
as avoid doing a read/modify/write on the BMCR register.

Doing a read/modify/write on the BMCR register means that the
auto-negotation bit may remain which interferes with the ability to put
the PHY into IDDQ-SR mode. We do software reset upon suspend in order to
put the PHY back into its state prior to suspend as recommended by the
datasheet.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>