x86/kexec: Fix bug with call depth tracking

In the Linux kernel, the following vulnerability has been resolved: x86/kexec: Fix bug with call depth tracking The call to cc_platform_has() triggers a fault and system crash if call depth tracking is active because the GS segment has been reset by load_segments() and GS_BASE is now 0 but call depth tracking uses per-CPU variables to operate. Call cc_platform_has() earlier in the function when GS is still valid. [ bp: Massage. ]