tsc2007: controlled removal and reduced number of I2C transactions

Two patches are supplied, booth are supposed to be applied against my previous ones, which are added to the -mm-tree.

The first one is proposed by Dmitry Torokhov, I have just made some changes so it applied to my previous changes, and I tried it out.

The second one decreases the number of I2C transactions transferred by the driver. A unnecessary one during probe and an unnecessary power down during each poll for coordinates are removed. The chip is explicitly powered down before waiting for interrupts.

--Richard