msm: emac: Improve external phy connect sequence

Currently PHY connect and disconnect are part of EMAC
driver Up and Down sequence.  Frequent PHY connect and
disconnect happens in error scenario which leads to
instability of Ethernet Link to external PHY.

So corrected below things as part of this patch:
(1) Avoid frequent phy connect and disconnect sequence
(2) Move EMAC regulators/clock control from Runtime to
system level PM framework. This will also reduce SGMII
link establishment time.
(3) Don’t allow SGMII PHY to go into power saving mode
in case it is connected to QCA8337 external switch
(4) Enable QCA8337 auto negotiation on Port0

Change-Id: I5435e4bde30f65e1e2a0062783b189160aa85c1b
Signed-off-by: Alok Chauhan <alokc@codeaurora.org>