x86/kexec: Keep CR4.MCE set during kexec for TDX guest

x86/kexec: Keep CR4.MCE set during kexec for TDX guest

TDX guests run with MCA enabled (CR4.MCE=1b) from the very start. If
that bit is cleared during CR4 register reprogramming during boot or kexec
flows, a #VE exception will be raised which the guest kernel cannot handle.

Therefore, make sure the CR4.MCE setting is preserved over kexec too and avoid
raising any #VEs.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240614095904.1345461-7-kirill.shutemov@linux.intel.com