x86/rethunk: Use SYM_CODE_START[_LOCAL]_NOALIGN macros

Macros already exist for unaligned code block symbols.  Use them.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/26d461bd509cc840af24c94586561c06d39812b2.1693889988.git.jpoimboe@kernel.org