net/smsc911x: Add regulator support

Add some basic regulator support for the power pins, as needed
by the ST-Ericsson Snowball platform that powers up the SMSC911
chip using an external regulator.

Platforms that use regulators and the smsc911x and have no defined
regulator for the smsc911x and claim complete regulator
constraints with no dummy regulators will need to provide it, for
example using a fixed voltage regulator. It appears that this may
affect (apart from Ux500 Snowball) possibly these archs/machines
that from some grep:s appear to define both CONFIG_SMSC911X and
CONFIG_REGULATOR:

- ARM Freescale mx3 and OMAP 2 plus, Raumfeld machines
- Blackfin
- Super-H

Cc: Paul Mundt <lethal@linux-sh.org>
Cc: linux-sh@vger.kernel.org
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Tony Lindgren <tony@atomide.com>
Cc: linux-omap@vger.kernel.org
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: uclinux-dist-devel@blackfin.uclinux.org
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Robert Marklund <robert.marklund@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>