staging: android: ashmem: Get rid of the big mutex lock

Ashmem uses a single big mutex lock for all synchronization, and even
uses it when no synchronization issues are present. The contention from
using a single lock results in all-around poor performance.

Use fine-grained locks and atomic constructions to eliminate the big
mutex lock, thereby improving performance greatly.

Signed-off-by: Sultan Alsawaf <[email protected]>
Signed-off-by: Danny Lin <[email protected]>
Signed-off-by: celtare21 <[email protected]>
Signed-off-by: Carlos Ayrton Lopez Arroyo <[email protected]>