Input: axp20x-pek - add support for AXP221 PEK

The AXP221 has different values for startup time bits from the AXP20X.

Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>