w1_therm: optimizing temperature read timings

Optimizing temperature reading by reducing waiting conversion time
according to device resolution settings, as per device specification.
This is device dependent as not all the devices supports resolution
setting, so it has been added in device family structures.

The process to read the temperature on the device has been adapted in a
new function 'convert_t()', which replace the former 'read_therm()', is
introduce to deal with this timing. Strong pull up is also applied during
the required time, according to device power status needs and
'strong_pullup' module parameter.

'temperature_from_RAM()' function is introduced to get the correct
temperature computation (device dependent) from device RAM data.

An new sysfs entry has been added to ouptut only temperature. The old
entry w1_slave has been kept for compatibility, without changing its
output format.

Updating Documentation/ABI/testing/sysfs-driver-w1_therm accordingly.
Signed-off-by: Akira Shimahara <akira215corp@gmail.com>
Link: https://lore.kernel.org/r/20200511203742.411039-1-akira215corp@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-driver-w1_therm

@@ -41,6 +41,18 @@ Users:		any user space application which wants to communicate with
 		w1_term device
 
 
+What:		/sys/bus/w1/devices/.../temperature
+Date:		May 2020
+Contact:	Akira Shimahara <akira215corp@gmail.com>
+Description:
+		(RO) return the temperature in 1/1000 degC.
+		Note that the conversion duration depend on the resolution (if
+		device support this feature). It takes 94ms in 9bits
+		resolution, 750ms for 12bits.
+Users:		any user space application which wants to communicate with
+		w1_term device
+
+
 What:		/sys/bus/w1/devices/.../w1_slave
 Date:		May 2020
 Contact:	Akira Shimahara <akira215corp@gmail.com>