rusty-gd: controller supported commands & le buffer sizes

also, generate TryFrom for OpCodeIndex from OpCode, to remove 700+ lines
of repeated code in C++ gd controller

Bug: 171749953
Tag: #gd-refactor
Test: gd/cert/run --rhost SimpleHalTest
Change-Id: Ic6d95ccc87a0ccc64636f16b0ef379c1f0d2f069