Keystore 2.0 SPI: Evolve the generator SPI.

We delegate the generation of self signed certificates to the KeyMint
backend. Also we use the KeyParamter AIDL type instead of
KeymasterArguments to construct parameter lists.

Bug: 159476414
Test: None
Change-Id: I441a4d4df4ef04e3da8aeaff3274c609d549c979