media: aspeed: Fix unstable timing detection

Using stable-signal in resolution detection, and try detection again
if unstable.

VE_MODE_DETECT_EXTSRC_ADC: 1 if video source is from ADC output.
VE_MODE_DETECT_H_STABLE: 1 if horizontal signal detection is stable.
VE_MODE_DETECT_V_STABLE: 1 if vertical signal detection is stable.

Signed-off-by: Jammy Huang <jammy_huang@aspeedtech.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>