char: fsl_otp: Enable kernel config option to enable write support

Write access to the fuses is very dangerous as they can only be
written once.  This is the first commit in locking this down a bit.
Now you must explicitely enable this functionality in the kernel.
char: fsl_otp: Add function to read otp values

Instead of having all drivers mapping the otp memory and checking
values provide a function so they can do it through the driver.
mach: imx: Use fsl_otp helper function

Instead of checking device-tree for the otp definition and mapping
memory ourselves, use the new helper function to read fuse values.
thermal: imx: Rework driver for better flexibility

This should probably be broken up into multiple patches but I will
do that when I get them ready for upstreaming.  Functionality that
I have added is follows.

- read grade of chip from otp and set critical based on this value.
- base the default passive trip points based on the number of cpu
frequency points and the critical thermal temperature.
- allow the user to change the trip_point0 up to a maximum of 85c
and then scale the trip points based on that.