binderRpcBenchmark: device tests kernel as ctrl

Host still tests RPC binder only since kernel binder is only on Android
(by convention!).

On local cuttlefish:

Tests suffixes:
        \0 is KERNEL
        \1 is RPC
...
---------------------------------------------------------------
Benchmark                     Time             CPU   Iterations
---------------------------------------------------------------
BM_pingTransaction/0      28448 ns        18366 ns        36940
BM_pingTransaction/1      39291 ns        26773 ns        25295
BM_repeatString/0        184458 ns        96268 ns         7263
BM_repeatString/1        206385 ns       116369 ns         5947
BM_repeatBinder/0         50475 ns        43567 ns        15896
BM_repeatBinder/1         50722 ns        44386 ns        15857

So the takeaway is that RPC binder has some overhead for very small
transactions.

Future considerations:
- make the RPC calls across processes instead of across threads
- see how scheduler optimizations affect this

Fixes: 194903439
Test: binderRpcBenchmark
Change-Id: Ib7b680091979d142bca4716d62cc579f90bade0f