vga: raise default vgamem size

Old size: 8 MB (traditional upstream qemu value).
New size: 16 MB (traditional qemu-kvm value).

Also adds compat properties so old machine types
keep the old default values.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/hw/vmware_vga.c b/hw/vmware_vga.c
index f8eb46d..476dc89 100644
--- a/hw/vmware_vga.c
+++ b/hw/vmware_vga.c
@@ -1201,7 +1201,7 @@
 
 static Property vga_vmware_properties[] = {
     DEFINE_PROP_UINT32("vgamem_mb", struct pci_vmsvga_state_s,
-                       chip.vga.vram_size_mb, 8),
+                       chip.vga.vram_size_mb, 16),
     DEFINE_PROP_END_OF_LIST(),
 };