soc: mediatek: mtk-mutex: Fix confusing usage of MUTEX_MOD2

soc: mediatek: mtk-mutex: Fix confusing usage of MUTEX_MOD2

The usage of MUTEX_MOD1 and MUTEX_MOD2 for calculating mod settings
over 32 has been confusing. To improve consistency and clarity, these
defines need to fit into the same MUTEX_MOD define as possible.

However, MUTEX_MOD1 cannot be directly used for all SoCs because,
for example, the mod1 register (0x34) of MT2712 is not adjacent to
its mod0 register (0x2c). To address this, a `mutex_mod1_reg` field
is introduced in the mutex driver data structure. This allows all
SoCs to use a unified MUTEX_MOD to determine their register offsets.

With this change, the separate usage of MUTEX_MOD1 and MUTEX_MOD2 is
eliminated, simplifying the logic for obtaining offsets and mod IDs.

Signed-off-by: Jason-JH Lin <jason-jh.lin@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20250624103928.408194-1-jason-jh.lin@mediatek.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>