st/va: hardlink driver instances to gallium_drv_video.so

Removes the need to set LIBVA_DRIVER_NAME=gallium for supported targets and is
consistent with vdpau and general gallium drivers.

Note: some versions of libva can detect the gallium name and use the
backend. Although that behaviour seems inconsistent since it only works
for some platforms/backends.

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

src/gallium/targets/va/Makefile.am

@@ -66,3 +66,17 @@ if HAVE_MESA_LLVM
 gallium_drv_video_la_LIBADD += $(LLVM_LIBS)
 gallium_drv_video_la_LDFLAGS += $(LLVM_LDFLAGS)
 endif
+
+# hardlink each megadriver instance, but don't actually have
+# gallium_drv_video.so in the set of final installed files.
+install-data-hook:
+	for i in $(TARGET_DRIVERS); do                                  \
+		ln -f $(DESTDIR)$(vadir)/gallium_drv_video.so                \
+		      $(DESTDIR)$(vadir)/$${i}_drv_video.so;                 \
+	done;                                                           \
+	$(RM) $(DESTDIR)$(vadir)/gallium_drv_video.*
+
+uninstall-hook:
+	for i in $(TARGET_DRIVERS); do                                  \
+		$(RM) $(DESTDIR)$(vadir)/$${i}_drv_video.so;                 \
+	done;