x86/microcode: Mark early_parse_cmdline() as __init

x86/microcode: Mark early_parse_cmdline() as __init

Fix section mismatch warning reported by modpost:

  .text:early_parse_cmdline() -> .init.data:boot_command_line

The function early_parse_cmdline() is only called during init and accesses
init data, so mark it __init to match its usage.

  [ bp: This happens only when the toolchain fails to inline the function and
    I haven't been able to reproduce it with any toolchain I'm using. Patch is
    obviously correct regardless. ]

Signed-off-by: Yu Peng <pengyu@kylinos.cn>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/all/20251030123757.1410904-1-pengyu@kylinos.cn