As the second and last step of preparation to add support for more
PMICs in this driver, move the long press debounce mask to struct
mtk_pmic_regs and use that in mtk_pmic_keys_lp_reset_setup() instead
of directly using the definition.

While at it, remove the definition for MTK_PMIC_RST_DU_SHIFT as we
are able to calculate it dynamically and spares us some unnecessary
new definitions around for future per-PMIC variations of RST_DU_MASK.

Lastly, it was necessary to change the function signature of
mtk_pmic_keys_lp_reset_setup() to now pass a pointer to the main
mtk_pmic_regs structure, since that's where the reset debounce
mask now resides.

This commit brings no functional changes.
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20220524093505.85438-3-angelogioacchino.delregno@collabora.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>