pmdomain: mediatek: Create bus protection operation functions

pmdomain: mediatek: Create bus protection operation functions

Separate the register access used for bus protection enable/disable into
their own functions. These will be used later for WAY_EN support.

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Tested-by: Alexandre Mergnat <amergnat@baylibre.com>
Link: https://lore.kernel.org/r/20230918093751.1188668-5-msp@baylibre.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>