enable kvm/testutil to support arm64
The Arm64 user-mode execution stat consists of:
1, X0- X30
2, PC, SP, PSTATE
3, TPIDR_EL0, used for TLS
4, V0-V31: 32 128-bit registers for floating point and simd
5, FPSR
Currently, we first try to achieve goals 1 and 2.
This patch provids basic test utils for goals 1 & 2
Signed-off-by: Bin Lu <bin.lu@arm.com>