Fix PDK build

This commit moves "IConfirmationPromptCallback.aidl" and
"IKeystoreService.aidl" to "system/security/keystore/binder" so that
"libkeystore_aidl" can be built in PDK builds.

Test: Run `cts-tradefed run cts -m CtsKeystoreTestCases` on Pixel 2017
and the test results are idential with and without this CL.

Test: Build PDK with special manifest described in
http://b/69539820#comment18 and http://b/69539820#comment19.

Test: Build a target (described in http://b/72961456) with
`platform.zip` built from master FSK source tree.

Bug: 69539820
Bug: 72961456
Change-Id: I7350f0ca943b15a6f3e40023a6cc299bdf8aed0e