Currently, only one debounce_interval is introduced for both direct and
matrix keys. This is true in most cases, although the keypad controller
supports different debounce for direct/matrix keys.

Some platforms do require this to be tuned, instead of the default
reset value of 100ms.

Rotary encoder will always use zero debounce time for now to achieve
certain sensitivity.
Signed-off-by: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>