Update checking debug.vulkan.layer.* system props

... to scan a fixed range of priorities followed by
consecutive priorities instead of scanning all system
props (property_list()) which causes sepolicy audits
when Vulkan is loaded in a process with a restrictive
sepolicy.

This avoids sepolicy audits in system_server for example
when running on Cuttlefish with SwANGLE (ANGLE GL on top
of SwiftShader Vulkan).

Bug: b/179967574
Test: boot Cuttlefish with SwANGLE and inspect audit logs
Change-Id: I63b3f45113fbdd3ab62c22f062150e25b99d7352