twl4030: move twl4030-pwrbutton to drivers/input/misc

Take it out of drivers/i2c/chips as requested by Jean Delvare
that all drivers move out of there.

Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Samuel Ortiz <sameo@openedhand.com>
Signed-off-by: Felipe Balbi <me@felipebalbi.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>