configs: use sha512 as default password hash

See this forum thread: https://forum.openwrt.org/t/passwd-a-sha256-sha512-less-secure-than-default/13117/9
1 job for master in 63 minutes and 18 seconds (queued for 2 minutes and 54 seconds)
Status Job ID Name Coverage
  Test
passed build-traverse-ls1088 #1407982595
x86 dynamic dynamic_runner_x86_aws

01:03:18