beep: fix dependency to support non-x86 target and kmod-gpio-beeper

beep: fix dependency to support non-x86 target and kmod-gpio-beeper

Beep is a target-independent software that can handle buzzers controlled by kmod-gpio-beeper.

This change is useful for some non-x86 enterprise APs and development boards
that have a buzzer connected to GPIO.

Compile-tested: ath79, ELECOM WAB-I1750-PS, 3fab4ac + device support patch
Run-tested: ath79, ELECOM WAB-I1750-PS, 3fab4ac + device support patch

Signed-off-by: Yanase Yuki <dev@zpc.sakura.ne.jp>
(cherry picked from commit 9bcea2de2cf552d544786d1e4b82f55cda7015b1)