x86/virt/tdx: Move low level SEAMCALL helpers out of <asm/tdx.h>

x86/virt/tdx: Move low level SEAMCALL helpers out of <asm/tdx.h>

TDX host core code implements three seamcall*() helpers to make SEAMCALLs
to the TDX module.  Currently, they are implemented in <asm/tdx.h> and
are exposed to other kernel code which includes <asm/tdx.h>.

However, other than the TDX host core, seamcall*() are not expected to
be used by other kernel code directly.  For instance, for all SEAMCALLs
that are used by KVM, the TDX host core exports a wrapper function for
each of them.

Move seamcall*() and related code out of <asm/tdx.h> and make them only
visible to TDX host core.

Since TDX host core tdx.c is already very heavy, don't put low level
seamcall*() code there but to a new dedicated "seamcall_internal.h".  Also,
currently tdx.c has seamcall_prerr*() helpers which additionally print
error message when calling seamcall*() fails.  Move them to
"seamcall_internal.h" as well. In such way all low level SEAMCALL helpers
are in a dedicated place, which is much more readable.

Copy the copyright notice from the original files and consolidate the
date ranges to:

	Copyright (C) 2021-2023 Intel Corporation

Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Vishal Annapurve <vannapurve@google.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://patch.msgid.link/20260520133909.409394-6-chao.gao@intel.com