build: Allow QC platforms to share/customize HAL variants

* Allow devices to override HAL variant using QCOM_HARDWARE_VARIANT
* 8909 and 8916 share HALs by default
* 8610, 8226, 8974 share HALs by default
* 8992, 8994 share HALs by default

Change-Id: Idfbdc405a35c5ba518fc71c8b691fc177ddf9068
(cherry picked from commit 338b399a2976993f0758c2f4e61620e987f4cb19)
1 file changed