Revert "pstore: Don't use semaphores in always-atomic-context code"

This reverts commit 86a926c3.

It breaks the abi and is not needed for Android devices so it can be
dropped.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I1583e40adde7173e3bd1283ea23feefe7c1e610c