x86/tdx: Add more registers to struct tdx_hypercall_args

struct tdx_hypercall_args is used to pass down hypercall arguments to
__tdx_hypercall() assembly routine.

Currently __tdx_hypercall() handles up to 6 arguments. In preparation to
changes in __tdx_hypercall(), expand the structure to 6 more registers
and generate asm offsets for them.

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/20230126221159.8635-3-kirill.shutemov%40linux.intel.com