cpu_load_efer is now used only for sysemu code.

Therefore, move this function implementation to
sysemu-only section of helper.c

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210322132800.7470-22-cfontana@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>