target/i386/sev: Rename sev_i386.h -> sev.h

target/i386/sev: Rename sev_i386.h -> sev.h

SEV is a x86 specific feature, and the "sev_i386.h" header
is already in target/i386/. Rename it as "sev.h" to simplify.

Patch created mechanically using:

  $ git mv target/i386/sev_i386.h target/i386/sev.h
  $ sed -i s/sev_i386.h/sev.h/ $(git grep -l sev_i386.h)

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20211007161716.453984-15-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>