Move sthal_cli under 2.4

This version is specifically a mock of STHAL 2.4, so it makes more
sense to put it under 2.4 and name it as such.

I intend to add a separate mock for the AIDL version, so making sure
the two don't collide.

Test: Ran the mock HAL and manually verified operation.
Change-Id: Ica8e53b981d73737bfb1720628592e650fc86ee0