I was debugging some gpio issues and I thought that the output of gpio
debugfs was telling me the high or low level of the gpios with a '1' or
a '0'. We saw a line like this though:

 gpio93  : in 4 2mA pull down

and I started to think that there may be a gas leak in the building
because '4' doesn't mean high or low, and other pins said '0' or '1'. It
turns out, '4' is the function selection for the pinmux of the gpio and
not the value on the pin. Reading code helps decipher what debugfs is
actually saying.

Add support to read the input or output pin depending on how the pin is
configured so we can easily see the high or low value of the pin in
debugfs. Now the output looks like

 gpio93  : in   low  func4 2mA pull down

which clearly shows that the pin is an input, low, with function 4 and a
2mA drive strength plus a pull down.

Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Alexandru M Stan <amstan@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>