ANDROID: x86/tdx: Move virt exception handler code to virt_exception.c

The TDX using virt exception to handle mmio opeartion, since virt
exception is a cpu feature, it can also being used by other cc_platform.
So move the common virt exception handler code to virt_exception.c

Bug: 395299836
Test: Boot, verify cpus are de-privileged and run a minimal protected vm.

Change-Id: Ia1acbe9949e380f8a0b9b5a5a7073399ed39606e
Signed-off-by: Shaoqin Huang <shaoqin.huang@intel.com>
Reviewed-by: Jason Chen CJ <jason.cj.chen@intel.com>
Signed-off-by: Vineeth Pillai <vineethrp@google.com>