i386: split smm helper (sysemu)

i386: split smm helper (sysemu)

smm is only really useful for sysemu, split in two modules
around the CONFIG_USER_ONLY, in order to remove the ifdef
and use the build system instead.

add cpu_abort() when detecting attempts to enter SMM mode via
SMI interrupt in user-mode, and assert that the cpu is not
in SMM mode while translating RSM instructions.

Signed-off-by: Claudio Fontana <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-Id: <20210322132800[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>