pvg: do not enable it on cross-architecture targets

PVG is not cross-architecture; the PVG guest drivers with x86-64 macOS do not give
useful results with the aarch64 macOS host PVG framework, and vice versa.
To express this repurpose CONFIG_MAC_PVG, making it true only if the target has
the same architecture as the host.  Furthermore, remove apple-gfx.m unless
one of the devices is actually present.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Kconfig.host

@@ -61,3 +61,6 @@ config HV_BALLOON_POSSIBLE
 
 config HAVE_RUST
     bool
+
+config MAC_PVG
+    bool

hw/display/Kconfig

@@ -141,10 +141,6 @@ config XLNX_DISPLAYPORT
 config DM163
     bool
 
-config MAC_PVG
-    bool
-    default y
-
 config MAC_PVG_MMIO
     bool
     depends on MAC_PVG && AARCH64

hw/display/meson.build

@@ -61,12 +61,9 @@ system_ss.add(when: 'CONFIG_ARTIST', if_true: files('artist.c'))
 
 system_ss.add(when: 'CONFIG_ATI_VGA', if_true: [files('ati.c', 'ati_2d.c', 'ati_dbg.c'), pixman])
 
-if host_os == 'darwin'
-  system_ss.add(when: 'CONFIG_MAC_PVG',         if_true: [files('apple-gfx.m'), pvg, metal])
-  system_ss.add(when: 'CONFIG_MAC_PVG_PCI',     if_true: [files('apple-gfx-pci.m'), pvg, metal])
-  if cpu == 'aarch64'
-    system_ss.add(when: 'CONFIG_MAC_PVG_MMIO',  if_true: [files('apple-gfx-mmio.m'), pvg, metal])
-  endif
+if pvg.found()
+  system_ss.add(when: 'CONFIG_MAC_PVG_PCI',     if_true: [files('apple-gfx.m', 'apple-gfx-pci.m'), pvg, metal])
+  system_ss.add(when: 'CONFIG_MAC_PVG_MMIO',    if_true: [files('apple-gfx.m', 'apple-gfx-mmio.m'), pvg, metal])
 endif
 
 if config_all_devices.has_key('CONFIG_VIRTIO_GPU')

meson.build

@@ -3367,6 +3367,12 @@ foreach target : target_dirs
     target_kconfig += 'CONFIG_' + config_target['TARGET_ARCH'].to_upper() + '=y'
     target_kconfig += 'CONFIG_TARGET_BIG_ENDIAN=' + config_target['TARGET_BIG_ENDIAN']
 
+    # PVG is not cross-architecture.  Use accelerator_targets as a proxy to
+    # figure out which target can support PVG on this host
+    if pvg.found() and target in accelerator_targets.get('CONFIG_HVF', [])
+      target_kconfig += 'CONFIG_MAC_PVG=y'
+    endif
+
     config_input = meson.get_external_property(target, 'default')
     config_devices_mak = target + '-config-devices.mak'
     config_devices_mak = configure_file(