Input: mt6779-keypad - prepare double keys support with calc_row_col

Input: mt6779-keypad - prepare double keys support with calc_row_col

The MediaTek keypad can operate in two modes: single key or double key.
The driver only supports single key mode. In double key mode, the
row/column calculation based on the key is different.

Add a calc_row_col function pointer which will be different based on
single/double key mode.

No functional change.

Suggested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220720-mt8183-keypad-v2-4-6d42c357cb76@baylibre.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>