Input: use for_each_set_bit() where appropriate

Instead of iterating over all bits in a bitmap and test them individually
let's siwtch to for_each_set_bit() which is more compact and is also
faster.

Also use bitmap_weight() when counting number of set bits.

This also fixes INPUT_DO_TOGGLE() implementation as it should have used
*_CNT as the upper boundary, not *_MAX.

Signed-off-by: Anshul Garg <aksgarg1989@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>