<rdar://problem/12491387>

Added commands to the KDP plug-in that allow sending raw commands through the KDP protocol. You specify a command byte and a payload as ASCII hex bytes, and the packet is created with a valid header/sequenceID/length and sent. The command responds with a raw ASCII hex string that contains all bytes in the reply including the header.

An example of sending a read register packet for the GPR on x86_64:

(lldb) process plugin packet send --command 0x07 --payload 0100000004000000

llvm-svn: 166346