Use the hwmon interface to expose the internal temperature sensor
connected to the ADC. In order to calculate the temperature typical
values from the electrical data sheet has been taken.

Read the sensor using sysfs:
$ cat /sys/class/hwmon/hwmon0/device/temp1_input
47282

Note: there are two hwmon devices exposed. Those are the two ADC,
however, both ADC connect to the same temperature sensor.
Essentially, the user can choose which ADC to use to read the
temperature sensor.

Enable support for all 32 ADC channels, even the internal one. This
is needed to read out the internal temperature since the sensor is
at channel 26.

Several registers in adc_set were set logical inverse or even the wrong
bits in the registers. Also, return the users ioctrl if the configuration
is not valid.

Do not return conversion before freeing the allocated memory.

When compiled as a module, the driver removes the device
entries correctly when the module exits.

The touchscreen support backed by hardware on the Colibri VF50
module and the Vybrid ADC is now moved to a own module for better
maintainability. The mvf-adc driver exports some of its method
now. A good good locking mechanism is still missing.

In order to be more energy efficient sample the ADC channels only
if touch is detected. Do the pinmux in the platform specific code,
extended the platform data with those helper functions.

Measure pressure between the two plates (z1/z2) and calculate
resistance which is an approximation measure of the pressure on
the touch screen. Improved signal by better ADC configuration
and averaging.

The Vybrid VF50 support 4-wire touchscreens using FETs and
ADC inputs. This drivers extends the ADC driver to deliver
initial support for this interface.

Extended driver to allow the use of multiple ADC devices. Tested
on Vybrid, works with two ADC instances.