gpio: ml-ioh: share the register lock across channels

gpio: ml-ioh: share the register lock across channels

Suspend and resume hold channel 0's lock while saving and restoring
registers for all eight channels. Code paths using the other seven locks
can therefore run concurrently with PM.

Use one controller-wide lock shared by all channels.

Fixes: b490fa0bf86e ("gpio-ml-ioh: Fix suspend/resume issue")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/r/20260731033956.EE6F61F000E9@smtp.kernel.org
Signed-off-by: Junjie Cao <junjie.cao@intel.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/20260804095935.2132215-1-junjie.cao@intel.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>