HVM cleanups:

HVM cleanups:
1) make vmx/svm time functions hvm common, since they are actually the same.
2) move hvm_send_assist_req from platform.c to hvm.c.
2) rename VMX MSR context switch functions to make them more readable.
3) misc coding style clean ups.

Signed-off-by: Xin Li <xin.b.li@intel.com>