anv: Enable SPV_KHR_16bit_storage and VK_KHR_16bit_storage for SSBO/UBO

anv: Enable SPV_KHR_16bit_storage and VK_KHR_16bit_storage for SSBO/UBO

Enables SPV_KHR_16bit_storage on gen 8+.

VK_KHR_16bit_storage is enabled for SSBO/UBO using the
VK_KHR_get_physical_device_properties2 functionality to expose
if the extension is supported or not.

v2: update due rebase against master (Alejandro)
v3: (Jason Ekstrand)
    - Move this patch up in VK_KHR_16bit_storage series enabling only
      storageBuffer16BitAccess and uniformAndStorageBuffer16BitAccess.
    - Only expose VK_KHR_16bit_storage on Gen8+
v4: (Jason Ekstrand)
    - Squash enable SPV_KHR_16bit_storage into VK_KHR_16bit_storage
      enablement for SSBO/UBO.

Signed-off-by: Jose Maria Casanova Crespo <jmcasanova@igalia.com>
Signed-off-by: Alejandro Piñeiro <apinheiro@igalia.com>
Signed-off-by: Eduardo Lima Mitev <elima@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>