libbinder: RPC avoid poll

One of the major costs of RPC binder right now, compared to kernel
binder, is that we need to make two calls (poll + recv) whereas regular
binder can make one (ioctl) in order to read or write a command.

By removing this, we can get more comparable performance:
        .../0 is KERNEL
        .../1 is RPC

------------------------------------------------------------------------------------
Benchmark                                          Time             CPU   Iterations
------------------------------------------------------------------------------------
BM_pingTransaction/0                           37075 ns        18940 ns        36734
BM_pingTransaction/1                           43729 ns        22184 ns        29429
BM_repeatTwoPageString/0                      266736 ns       133091 ns         5273
BM_repeatTwoPageString/1                      311444 ns       155527 ns         5016
BM_throughputForTransportAndBytes/0/64         43458 ns        22226 ns        28221
BM_throughputForTransportAndBytes/1/64         49153 ns        25038 ns        36104
BM_throughputForTransportAndBytes/0/1024       44020 ns        22418 ns        26449
BM_throughputForTransportAndBytes/1/1024       49634 ns        25554 ns        30230
BM_throughputForTransportAndBytes/0/2048       41932 ns        21246 ns        34684
BM_throughputForTransportAndBytes/1/2048       49055 ns        24907 ns        29689
BM_throughputForTransportAndBytes/0/4096       49634 ns        25179 ns        26992
BM_throughputForTransportAndBytes/1/4096       53318 ns        27001 ns        20076
BM_throughputForTransportAndBytes/0/8182       59537 ns        30068 ns        26722
BM_throughputForTransportAndBytes/1/8182       69677 ns        35005 ns        19992
BM_throughputForTransportAndBytes/0/16364      67281 ns        30455 ns        24654
BM_throughputForTransportAndBytes/1/16364      86123 ns        42752 ns        18558
BM_throughputForTransportAndBytes/0/32728      83229 ns        37705 ns        16238
BM_throughputForTransportAndBytes/1/32728     116709 ns        57592 ns        12981
BM_throughputForTransportAndBytes/0/65535     223220 ns       104757 ns         6015
BM_throughputForTransportAndBytes/1/65535     380800 ns       187026 ns         4544
BM_throughputForTransportAndBytes/0/65536     202564 ns        95486 ns         7548
BM_throughputForTransportAndBytes/1/65536     347559 ns       170957 ns         4795
BM_throughputForTransportAndBytes/0/65537     293614 ns       128131 ns         5816
BM_throughputForTransportAndBytes/1/65537     524383 ns       241437 ns         2927
BM_repeatBinder/0                              62491 ns        33405 ns        19466
BM_repeatBinder/1                              68013 ns        33611 ns        23083

Bug: 182940634
Test: binderRpcBenchmark (above)
Change-Id: I5cbaf40e5936bdce04b5f158ceac970e8f6ff2fa