x86/platform/amd: Clean up the <asm/amd/hsmp.h> header guards a bit

 - There's no need for a newline after the SPDX line
 - But there's a need for one before the closing header guard.

Collect AMD specific platform header files in <asm/amd/*.h>.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Carlos Bilbao <carlos.bilbao@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mario Limonciello <superm1@kernel.org>
Cc: Naveen Krishna Chatradhi <naveenkrishna.chatradhi@amd.com>
Link: https://lore.kernel.org/r/20250413084144.3746608-6-mingo@kernel.org