Backport of lm77.c from kernel 2.6.x to 2.4.x

This is a Linux kernel 2.4 driver for the LM77, a temperature sensor and thermal window comparator with 0.5 deg resolution made by National Semiconductor. Actually it's a backport of lm77.c from kernel 2.6.

lm77-2.4 is in production use by the sponsor of the backport effort, true global communications GmbH. It's known to basically work in conjunction with lm_sensors v2.9.2. However, there is evidence that there might be some bugs, but I'm not sure if they are caused by the LM77 driver or the I2C bus driver that we use. I never found the time to investigate this issue so far.

Please note that I didn't actively work on the driver since years. In particular I didn't track changes that might have happened to lm77.c in kernel 2.6 and later. You will also be on your own so far regarding the integration of the driver into the lm_sensors package, but that shouldn't be too hard.