hw/core: Restrict 'fw-path-provider.c' to system mode emulation

fw-path-provider.c is only consumed by qdev-fw.c, which itself
is in softmmu_ss[], so we can restrict fw-path-provider.c to
softmmu too.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20201207220709.4017938-1-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/core/meson.build

 # core qdev-related obj files, also used by *-user and unit tests
 hwcore_files = files(
   'bus.c',
-  'fw-path-provider.c',
   'hotplug.c',
   'qdev-properties.c',
   'qdev.c',
@@ -25,6 +24,7 @@ common_ss.add(when: 'CONFIG_SPLIT_IRQ', if_true: files('split-irq.c'))
 common_ss.add(when: 'CONFIG_XILINX_AXI', if_true: files('stream.c'))
 
 softmmu_ss.add(files(
+  'fw-path-provider.c',
   'loader.c',
   'machine-hmp-cmds.c',
   'machine.c',