counter: 104-quad-8: Add lock guards - generic interface

Add lock protection from race conditions to 104-quad-8 counter driver
generic interface code changes. Mutex calls used for protection.

Fixes: f1d8a071 ("counter: 104-quad-8: Add Generic Counter interface support")
Signed-off-by: Syed Nayyar Waris <syednwaris@gmail.com>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>