Fix keystore wifi concurrency issue.

Keystore was conceptually single threaded. Even with the introduction of
Keymaster workers it was always assumed that the service dispatcher
thread was single threaded. The wifi keystore service, however, calls
into the keystore service concurrently.

This patch adds a lock around all keystore service entry points to make
sure all dispatcher executions are serialised despite being called from
both the binder and hwbinder service thread.

Bug: 128810613
Bug: 129145334
Bug: 128774635
Test: Regressions tested with Keystore CTS test suite.
Change-Id: I8c5602d2c2cb1dd9423df713037e99b247cee71f