Snap: Fix getting supported ISO with legacy HAL

 * org.codeaurora.qcamera3.iso_exp_priority.iso_available_modes is QCOM
   specific vendor tag and not implemented in legacy HALs.
 * Restore pre-17.0 behavior by falling back to AOSP camera characteristics

Change-Id: I299e7bfb867496c63ec873ea4cea29b0b8bb595f
1 file changed