[MIPS64] Create a wrapper for running MIPS64 ranchu QEMU

MIPS64 Android emulation will be run on the new code base QEMU
which implements new virtual board called "ranchu".
This commit adds new build products to external/qemu named
emulator-mips64 and emulator64-mips64 which will be wrappers
for parsing the "emulator" command line arguments to build
standard QEMU command line for running the emulation.

Change-Id: Iadac4481c54c11c43699eda73326e2476e900618
Merge "[MIPS64] Create a wrapper for running MIPS64 ranchu QEMU"