vl: Set errp to &error_abort on machine compat_props

Use the new GlobalProperty.errp field to handle compat_props
errors.

Example output before this change:
(with an intentionally broken entry added to PC_COMPAT_1_3 just
for testing)

  $ qemu-system-x86_64 -machine pc-1.3
  qemu-system-x86_64: hw/core/qdev-properties.c:1091: qdev_prop_set_globals_for_type: Assertion `prop->user_provided' failed.
  Aborted (core dumped)

After:

  $ qemu-system-x86_64 -machine pc-1.3
  Unexpected error in x86_cpuid_set_vendor() at /home/ehabkost/rh/proj/virt/qemu/target-i386/cpu.c:1688:
  qemu-system-x86_64: can't apply global cpu.vendor=x: Property '.vendor' doesn't take value 'x'
  Aborted (core dumped)

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
