MAINTAINERS: Add x86 hardware vulnerabilities section

Add the bunch of losers who have to deal with this to MAINTAINERS so
that they can get explicitly CCed on more hw nightmares.

  [ bp: Add commit message. ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230224213522.nofavod2jzhn22wp@treble