Inject CPU options to spike run test from elf file

* Refactor CPU options for exacting common part between qemu and spike.
* Inject CPU options to spike run command line.

The below common CPU options are extracted to common part.

* xlen
* vlen
* extensions

The above CPU options will be leveraged to build the run arguments for
both the qemu and spike, for example.

QEMU: qemu-riscv64 -cpu rv64,v=true,vlen=1024,elen=64,vext_spec=v1.0
SPIKE: spike --isa=rv64imafdcv_zicsr_zifencei_zmmul --varch=vlen:1024,elen:64

Signed-off-by: Pan Li <pan2.li@intel.com>