x86/bugs: Split spectre_v2_select_mitigation() and spectre_v2_user_select_mitigation()

x86/bugs: Split spectre_v2_select_mitigation() and spectre_v2_user_select_mitigation()

commit e03a63d698eb151ee8462b84edf494e73c776a8f upstream.

retbleed will depend on spectre_v2, while spectre_v2_user depends on
retbleed. Break this cycle.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>