remoteproc: mediatek: Extract SCP common registers

remoteproc: mediatek: Extract SCP common registers

This is the 1st preliminary steps for probing multi-core SCP.
The registers of config and l1tcm are common on single-core SCP
and multi-core SCP. Extract these registers out to reduce duplicated
fields in mtk_scp when multiple SCP instances are created.

Signed-off-by: Tinghan Shen <tinghan.shen@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230901080935.14571-6-tinghan.shen@mediatek.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>