devicetree: bindings: Properly document micrel ks8851 SPI chips

The ks8851 SPI ethernet wasn't documented, but we documented the
optional regulator supply for it under the mll based ethernet
chip. Furthermore, that compatible string needed another 'l'. Fix
all of this and document the optional vdd-io and reset-gpios
properties.

Cc: Nishanth Menon <nm@ti.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: <devicetree@vger.kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>