x86/tdx: Expand __tdx_hypercall() to handle more arguments

So far __tdx_hypercall() only handles six arguments for VMCALL.
Expanding it to six more register would allow to cover more use-cases
like ReportFatalError() and Hyper-V hypercalls.

With all preparations in place, the expansion is pretty straight
forward.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20230126221159.8635-5-kirill.shutemov%40linux.intel.com